Backseamed casing and packaged product incorporating same

ABSTRACT

A heat-shrinkable backseamed casing film comprises a first layer, a second layer, and a third layer, with the first and third layers being outer layers and the second layer being between the first layer and the third layer. The first outer layer serves as an inside casing layer, and comprises polyolefin; the second layer comprises polyester and/or polyamide; the third layer serves as an outside casing layer and comprises polyolefin, polystyrene, and/or polyamide. The second layer has a thickness of at least about 5% of a total thickness of the heat-shrinkable casing film. Alternatively, the first layer comprises polyolefin and has a surface energy level of less than about 34 dynes/cm; the second layer comprises a polyamide having a melting point of at least 300° F.; and the third layer comprises polyolefin, polystyrene and/or polyamide. A package comprises a cooked meat product within the backseamed casing. The second layer of the casing film prevents or reduces necking down on the forming shoe during backseaming. The backseamed casing is especially useful for cook-in applications.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 08/968,016, filedNov. 12, 1997, now U.S. Pat. No. 6,221,410, which is a continuation ofU.S. Ser. No. 08/539,919, filed Oct. 6, 1995, now abandoned, which is acontinuation-in-part of U.S. Ser. No. 07/951,245, filed Sep. 25, 1992,now abandoned, and a continuation-in-part of U.S. Ser. No. 07/893,638,filed Jun. 6, 1992, now abandoned.

FIELD OF THE INVENTION

The present invention relates generally to multilayer films, andparticularly to multilayer films suitable for use in backseamed casingsfor packaging meat products. The present invention is particularlyrelated to backseamed casings suitable for packaging protein-containingfood products in which the film adheres to the food product, andespecially to those having a relatively high protein content, alsocalled ‘low-fat’ food products, such as poultry, ham, roast beef, etc.The present invention is also directed to packages.

BACKGROUND OF THE INVENTION

Processed meat products, such as poultry and ham, are often packaged ina flexible, thermoplastic, heat-shrinkable film tubing commonly referredto as a casing. Although some casings have a lay-flat width of 6-20inches, some products, such as ham, etc., are quite often packaged in acasing of smaller lay-flat width, e.g., a width of from about 3 to 6inches. Such casings often may need to have a precisely-controlledwidth, because the packages are stated as having a given weight, whichis uniform among packages, and the packages also have product sliced atuniform intervals, with each package containing the same number ofslices. Thus, variations in casing width can result in both anundesirable degree of variation in overall package weight, as well as anundesirable degree of variation in slice weights.

Thus, there is a need for a casing having a small and uniform diameter.However, it is relatively difficult to make a narrow width,heat-shrinkable seamless casing having a precisely controlled width,using a commercially feasible process. Consequently, there is a need forsome other process for making a narrow-width, precisely-width-controlledcasing.

Some backseamed casings are known to be casings of small and uniformdiameter. Small-diameter backseamed casings are known which have aprecisely controlled casing width, i.e., a lay-flat width independent offilm extrusion variations. In the production of backseamed casings(e.g., using a backseaming machine such as a Nishibe HSP-250-SAbackseaming machine obtained from Nishibe Kikai Co. Ltd. of Nagoya,Japan), a flat sheet of film is folded longitudinally by passage over a“forming shoe”. A forming shoe is a part of the backseaming machinewhich the film is passed under and around, i.e., so that the initiallyflat film is reconfigured as a tube, having a longitudinal overlap andseal therealong (lap-sealed backseamed casing), or with filmlongitudinal edges abutted against one another (butt-sealed backseamedcasing), with the width of the tube being determined by thecircumference of the forming shoe. A longitudinal lap or butt seal isthen applied while the film is between the forming shoe and a sealingdevice, resulting in a lap-sealed backseamed casing, or a butt-sealedbackseamed casing. Butt-seal casings utilize a butt-seal tape sealed tothe inside or the outside surface of the casing film, along both sidesof the abutting longitudinal seam of the casing film. In either event,the resulting tubing, termed a “backseamed casing,” is sealed or clippedat its ends after being filled with a meat product. For some uses, themeat product is thereafter cooked while in the backseamed casing.

It would be desirable to provide a highly uniform, small diameterbackseamed casing suitable for cook-in end use, the casing being madefrom a film which adheres to high-protein meat products, such as certaingrades of ham and turkey. Of course, it would also be desirable toprovide the backseamed casing with a backseam seal which survives thecook-in process.

It is known that a polar surface is needed for adhesion of a film to ameat product. Adhesion of the film to the meat is frequently needed inorder to prevent “purge”, i.e., cook-out, which can occur during thecooking of the meat packaged in the film if the film does adhere to themeat during cook-in. A polar film surface can be provided by using: (a)polar resin in the film layer in contact with the meat, and/or (b)surface modification, such as corona treatment, of the film surface incontact with the meat. Typically, polar polymers used for meat adhesioninclude: ethylene/unsaturated acid copolymer, anhydride-containingpolyolefin, and polyamide.

Film-to-meat adhesion is known to be enhanced by corona treatment of thesurface of the film to which the meat is to be adhered. However, coronatreatment alters the film surface in a manner which can, on occasion,result in an inferior seal, i.e., a seal more likely to leak than if thefilm surface is not corona treated. This “leaky seal problem” can beavoided by “buffing off” the corona treatment in the area of the seal,so that the advantageous effects of the corona treatment, i.e., greatermeat adhesion, can be retained on the majority of the meat-contactsurface of the film, while at the same time avoiding, in the area of theseal, the seal-quality problem caused by the corona treatment. However,the buffing step is undesirable, as it is an additional processing stepwhich renders the casing manufacture more complex and costly.Furthermore, the buffing step is frequently inconsistent.

Since the backseaming process is generally carried out after the coronatreatment, shrinkage of the film against the forming shoe (duringbackseaming), coupled with forwarding the film over the forming shoeafter shrinkage, results in the rubbing of the film against the formingshoe edges. This rubbing reduces or destroys corona treatment, at leastin the area in which the film rubs against the forming shoe. As aresult, backseamed casings containing corona treated films can exhibitpurge at the locations at which the film rubs against the forming shoe.Furthermore, corona treatment can be inconsistent, at least with respectto prevention of purge for products having an intermediate proteincontent. It would be desirable that the casing film has a consistent andadequate level of protein/meat adhesion. As a result, it would bedesirable to provide a corona-treatment-free backseamed casing whichprevents purge from products relatively high in protein, where theadhesion of the casing film to the meat product is uniform over thefilm.

Thus, it would be desirable to provide a backseamed casing of small anduniform diameter which is heat-shrinkable and suitable for cook-in enduse, exhibits good purge-resistance and good seal strength, can beeconomically manufactured, does not produce significant meat pull-offupon being stripped from a cooked meat product, and which provides agood oxygen barrier, in order to provide good shelf life to the cookedmeat product.

Heat-shrinkable films having an outer layer capable of providing meatadhesion, which are otherwise suitable for use as backseamed casings,have been found to have the undesirable characteristic of necking downon the forming shoe during the backseaming process. The necking down onthe forming shoe is believed to be due to shrinkage of the film duringthe heat sealing step of the backseaming operation. That is, the heatsealing step can cause substantial film shrinkage in an area extendingoutward from the seal, causing the edges of the casing to neck down onthe forming shoe. The result of necking down is a casing having “rufflededges”, i.e., visible nonuniformities in the casing. In an extreme case,necking down results in the rupture of the film, as the shrinking of thefilm against the forming shoe places so much force on the film that thefilm ruptures. Thus, it would be desirable to provide a casing filmwhich does not shrink down (i.e., “neck down”) on the forming shoeduring the backseaming operation.

SUMMARY OF THE INVENTION

It has been discovered that the presence of an inner layer comprising apolyamide, preferably a high modulus polyamide, provides, if thepolyamide layer makes up at least 5 percent of the total film thickness,a film which does not neck down on the forming shoe during thebackseaming operation. Although the reasons why the inner polyamidelayer prevent necking down on the forming shoe are not currently knownwith certainty, it is believed that various factors, including heattransfer, shrink characteristics, etc. bring about the discoveredadvantage of not necking down on the forming shoe. Furthermore, theinner polyamide layer also helps to provide a better quality casing filmby making the casing film easier to orient, facilitating fasterbackseaming speeds, and also imparting enhanced seal strength,toughness, pin-hole resistance and elastic recovery to the casing film.

It has also been discovered that in the case of anhydride-containingpolyolefin, if the anhydride functionality is of the order of 1 weightpercent or less, the polymer often does not provide adequate meatadhesion to intermediate-protein-containing meat products, orlow-protein-containing meat products. On the other hand, polymers suchas polyamide can, in some instances, provide too much meat-adhesion andtend to pull meat off during unpackaging of the meat, thereby destroyingthe smooth surface desired upon separating the casing film from thecooked meat product, and also contributing to yield loss. Polyamides arealso relatively expensive polymers. Thus, it would be desirable toprovide a casing having a film providing adequate meat adhesion toprevent purge, while being able to strip the film from the meat withoutmeat pull-off due to too much adhesion of the film to the cooked meatproduct. However, it has been found that adequate meat adhesion can beobtained using an anhydride-containing polyolefin having an anhydridefunctionality of at least 1 percent.

As a first aspect, the present invention is directed to a backseamedcasing comprising a heat-shrinkable casing film. The heat shrinkablefilm comprises a first layer, a second layer, and a third layer, withthe first and third layers being outer layers and the second layer beingbetween the first layer and the third layer. The first outer layerserves as an inside casing layer, and comprises a first polyolefin. Thefirst polyolefin comprises at least one member selected from the groupconsisting of: (i) ethylene/unsaturated acid copolymer,propylene/unsaturated acid copolymer, and butene/unsaturated acidcopolymer, wherein the unsaturated acid is present in an amount of atleast 4 weight percent, based on the weight of the copolymer; and (ii)anhydride-containing polyolefin comprising an anhydride-functionality,wherein the anhydride functionality is present in an amount of at least1 weight percent, based on the weight of the anhydride-containingpolyolefin. The second layer comprises at least one member selected fromthe group consisting of polyester, and first polyamide. The third layerserves as an outside casing layer, and comprises at least one memberselected from the group consisting of second polyolefin, polystyrene,and second polyamide. The second layer has a thickness of at least about5% of a total thickness of the heat-shrinkable casing film.

In the first layer, the first polyolefin preferably comprises anethylene/unsaturated acid copolymer having an unsaturated acid merpresent in an amount of at least 6 percent, based on the weight of theethylene/unsaturated acid copolymer; more preferably, the unsaturatedacid is present in an amount of at least 9 weight percent, based on theweight of the ethylene/unsaturated acid copolymer.

The first layer preferably further comprises a third polyolefincomprising at least one member selected from the group consisting ofpolyethylene homopolymer, polyethylene copolymer, polypropylenehomopolymer, polypropylene copolymer, polybutene homopolymer, andpolybutene copolymer. More preferably, the third polyolefin comprises atleast one member selected from the group consisting ofethylene/alpha-olefin copolymer, propylene/alpha-olefin copolymer,butene/alpha-olefin copolymer, ethylene/unsaturated acid copolymer, andethylene/unsaturated ester copolymer. Still more preferably, the thirdpolyolefin comprises at least one member selected from the groupconsisting of linear low density polyethylene (LLDPE),propylene/ethylene copolymer, and propylene/butene copolymer. Yet stillmore preferably, the third polyolefin comprises LLDPE.

The second layer preferably comprises the first polyamide. Morepreferably, the first polyamide comprises at least one member selectedfrom the group consisting of polyamide 6, polyamide 66, polyamide 9,polyamide 10, polyamide 11, polyamide 12, polyamide 69, polyamide 610,polyamide 612, polyamide 6I, polyamide 6T, and copolymers thereof. Stillmore preferably, the first polyamide comprises at least one memberselected from the group consisting of polyamide 6, polyamide 66 andcopolyamide 6/66.

The third layer preferably comprises the second polyolefin. Preferably,the second polyolefin has a vicat softening point of at least 80° C.;more preferably, at least 90° C.; and still more preferably, at least100° C. The softening point of the second polyolefin has to be highenough to undergo cook-in without causing the seals to fail (if thepolyolefin is used in a seal layer). In an alternative preferredembodiment, the third layer comprises the second polyamide, with orwithout the second polyolefin, more preferably, as an alternative to thesecond polyolefin.

Preferably, the casing film further comprises a fourth layer, the fourthlayer being an inner layer serving as an O₂-barrier layer, the fourthlayer comprising at least one member selected from the group consistingof ethylene/vinyl alcohol copolymer, polyvinylidene chloride copolymer,polyethylene carbonate copolymer and polyamide. Preferably, the secondlayer and the fourth layer are directly adhered.

Preferably, the casing film further comprises a fifth layer and a sixthlayer, wherein: (a) the fifth layer is between the first layer and thesecond layer, and the sixth layer is between the second layer and thethird layer; (b) the fifth layer comprises at least one member selectedfrom the group consisting of fourth polyolefin, polystyrene andpolyurethane; and (c) the sixth layer comprises at least one memberselected from the group consisting of fifth polyolefin, polystyrene andpolyurethane. Preferably, the fifth layer is a tie layer and comprisesat least one member selected from the group consisting of modifiedethylene/alpha-olefin copolymer, modified ethylene/unsaturated estercopolymer, and modified ethylene/unsaturated acid copolymer. Preferably,the sixth layer is a tie layer and comprises at least one memberselected from the group consisting of modified ethylene/alpha-olefincopolymer, modified ethylene/unsaturated ester copolymer, and modifiedethylene/unsaturated acid copolymer.

Preferably, the casing film further comprises: (a) a seventh layer, theseventh layer being between the first layer and the second layer, theseventh layer comprising a sixth polyolefin; and (b) an eighth layer,the eighth layer being between the second layer and the third layer, theeighth layer comprising a seventh polyolefin.

Preferably, a ratio of: (a) a sum of the thickness of the first layerand the fifth layer; to (b) a sum of the thickness of the third layerand the sixth layer is from about 0.7:1 to 1.3:1. Preferably the secondlayer has a thickness of from about 5 to 20 percent, based on a totalthickness of the multilayer film; and preferably, the fourth layer has athickness of less than about 15%, based on a total thickness of themultilayer film. Preferably, the heat-shrinkable casing film has biaxialorientation. Preferably, the casing film has a free shrink, at 185° F.,of at least 10% in at least one direction. Preferably, at least aportion of the casing film comprises a crosslinked polymer network.

The backseamed casing according to the present invention can be either alap-sealed backseamed casing or a butt-sealed backseamed casing. Abutt-sealed casing comprises both a casing film and a butt-seal tapefilm. Preferably, the butt-seal tape film comprises at least one memberselected from the group consisting of polyolefin, polyamide orpolystyrene, and preferably the butt-seal tape film is heat-shrinkable.

As a second aspect, the present invention is directed to a packagecomprising a cooked meat product within a backseamed casing. Thebackseamed casing is according to the first or third aspects of thepresent invention described herein, and the cooked meat product isadhered to a meat-contact surface of the casing film.

Preferably, the meat product comprises at least one member selected fromthe group consisting of poultry, ham, beef, lamb, fish, liver sausage,bologna, mortadella, braunschweiger, goat, and horse; more preferably,poultry, ham, beef, lamb, fish, liver sausage, bologna, and mortadella.Preferably, the meat-contact surface of the first layer is coronatreated, and the meat product comprises at least one member selectedfrom the group consisting of liver sausage, bologna and mortadella.Preferably, the outside surface of the casing film is also coronatreated. Preferably, the meat comprises from 0-30% fat, more preferablyfrom 1-15% fat, still more preferably from 2-10% fat, and yet still morepreferably from 3-7% fat. Preferred backseamed casings for use in thepackage include the preferred backseamed casings in accordance with thepresent invention.

If a non-corona treated backseamed casing (or equivalent thereofaccording to the first aspect of the present aspect is used, the cookedmeat product preferably comprises at least one member selected from thegroup consisting of turkey, ham, beef, and fish, wherein the meatproduct comprises fat in an amount of from about 2 to 10 weight percent,preferably 3 to 8 percent, and more preferably from about 4 to 6percent. If a corona treated backseamed casing (or equivalent thereof)according to the first aspect of the present aspect is used, the cookedmeat product preferably comprises at least one member selected from thegroup consisting of ham, beef, liver sausage, bologna, mortadella,horse, and goat; more preferably, the meat product comprises at leastone member selected from the group consisting of ham, liver sausage,bologna, and mortadella; preferably, the cooked meat product comprisesfat in an amount of from about 3 to 40 weight percent, preferably 5 to30 percent, and more preferably from about 10 to 15 percent.

If a non-corona treated backseamed casing (or equivalent thereof)according to the third aspect of the present aspect is used, the cookedmeat product preferably comprises at least one member selected from thegroup consisting of turkey and fish, wherein the meat product comprisesfat in an amount of from about 1 to 10 weight percent, preferably 2 to 6percent, and more preferably from about 3 to 5 percent.

As a third aspect, the present invention is directed to a backseamedcasing comprising a heat-shrinkable casing film comprising: (A) a firstouter layer serving as an inside casing layer, the first outer layercomprising a first polyolefin, the first outer layer having a surfaceenergy level of less than about 34 dynes/cm; (B) a second layercomprising a first polyamide having a melting point of at least 300° F.;(C) a third layer serving as an outside casing layer, the third outerlayer comprising at least one member selected from the group consistingof a second polyolefin, polystyrene and second polyamide. The secondlayer is between the first layer and the third layer, and the secondlayer has a thickness of at least about 5% of a total thickness of theheat-shrinkable casing film.

In a lap-sealed backseamed casing according to this third aspect of thepresent invention, preferably the first polyolefin has a vicat softeningpoint of at least 70° C., more preferably at least 80° C., in order toprovide a desired level of seal strength. However, in a butt-sealedbackseamed casing according to this third aspect of the presentinvention, the vicat softening point of the first polyolefin may be lesscritical. More preferably, the first polyolefin is a relativelynon-polar polymer, preferably having a surface energy level of less than32 dynes/cm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a lap-seal backseamedcasing in accord with the present invention.

FIG. 2 illustrates an enlarged cross-sectional view of a first preferredcasing film suitable for use in the lap-seal backseamed casingillustrated in FIG. 1.

FIG. 3 illustrates an enlarged cross-sectional view of a secondpreferred casing film suitable for use in the lap-seal backseamed casingillustrated in FIG. 1.

FIG. 4 illustrates an enlarged cross-sectional view of a third preferredcasing film suitable for use in the lap-seal backseamed casingillustrated in FIG. 1.

FIG. 5 illustrates a cross-sectional view of a butt-seal backseamedcasing in accord with the present invention.

FIG. 6 illustrates an enlarged cross-sectional view of a first preferredcasing film suitable for use in the butt-seal backseamed casingillustrated in FIG. 5.

FIG. 7 illustrates an enlarged cross-sectional view of a first preferredbutt-seal tape film suitable for use in the butt-seal backseamed casingillustrated in FIG. 5.

FIG. 8 illustrates a schematic view of a process for making a preferredheat-shrinkable casing film and/or butt-seal tape film, for use in abackseamed casing in accord with the present invention.

FIG. 9 illustrates a perspective view of a first package according tothe present invention.

FIG. 10 illustrates a perspective view of a second package according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “package” and the phrase “packaged product”refer to an article in which a product (preferably a food product, morepreferably a meat-containing food product) is encased in a packagingfilm.

As used herein, the phrase “lay-flat film” refers to a film that hasbeen extruded as a wide, thin-walled, circular tube, usually blown,cooled, then gathered by converging sets of rollers and wound up inflattened form. The phrase “lay-flat width”, refers to half of thecircumference of the inflated film tube.

As used herein, the phrase “backseamed casing” refers to any casing (atubular film) having a longitudinal seal. For example, a lap-sealbackseamed casing can be formed: by folding a film strip over a formingshoe of a horizontal sealing machine, and applying a longitudinal sealthereto where the film overlaps, e.g. using a Nishibe Model HSP-250-SAsealing machine; or a Totani Model FD-350C sealing machine obtained fromTotani Giken Kogyo Co., Ltd., of Kyoto, Japan; or, by folding a filmstrip over a forming shoe of a vertical form fill and seal machine, andapplying a longitudinal seal thereto where the film overlaps, e.g.,using an ONPACK-2002 (TM) sealing machine, obtained from OrihiroCompany, Ltd., of Tomioka City, Japan. A lap-sealed casing could alsouse a tape-film in between the areas where the film overlaps, tofacilitate sealing. A butt-seal backseamed casing can be formed: byfolding a film strip over a forming shoe of a horizontal sealingmachine, with opposing longitudinal edges abutting one another, i.e., innon-overlapping relation to one another; and thereafter, by applying abutt-seal tape film over the abutting edges, followed by sealing thebutt-seal tape film across and along the abutting edges, so that asealed tube is formed.

For the backseamed casings according to the present invention, thecomposition in the second layer can be present either in one or morelayers of the casing film. If the composition is present in more thanone layer, the layers are preferably so positioned as to providereasonable symmetry to the film, thus providing a relatively flat,curl-free film.

Preferably, the backseamed casing according to the present invention hasa lay-flat width of at less than about 10 inches; more preferably, fromabout 1 to 10 inches, still more preferably, from about 2 to 8 inches;yet still more preferably, from about 3 to 7 inches, and yet still evenmore preferably, from about 4 to 6 inches. It is believed that for anygiven film to be backseamed, the problem of necking down on the formingshoe becomes worse as the lay-flat width of the casing is reduced.

Heat-shrinkable multilayer films of the invention preferably have asubstantially symmetrical cross-section, with respect to both layerthickness and layer chemical composition, in order to provide the filmwith relatively low curl. For example, for a 3-layer casing filmaccording to the backseamed casing of the present invention, the ratioof a/b is preferably from about 0.7-1.3, more preferably from about0.8-1.2, and even more preferably from about 0.9-1.1; wherein, ‘a’ isthe thickness of the first outer layer and ‘b’ is the thickness of thesecond outer layer. For a preferred six-layer casing film in accordancewith the backseamed casing of the present invention, the ratio of thesums of the thickness of the first layer plus the fifth layer to the sumof the second layer plus the sixth layer is preferably from about0.7-1.3; more preferably from about 0.8 to 1.2; and still morepreferably, from about 0.9 to 1.1.

The heat-shrinkable casing film according to the present inventionpreferably has a free shrink of from about 5-70 percent in one or bothdirections (i.e., longitudinal direction “L”, also referred to as“machine direction”, and transverse direction, “T”) at 185° F.,determined according to ASTM D 2732; more preferably, from about 10-50percent at 185° F.; still more preferably, from about 15-35 percent at185° F. Preferably, the casing film is biaxially oriented, andpreferably the film has a free shrink, at 185° F., of at least 10percent in each direction (L and T); more preferably, at least 15percent in each direction. Preferably, the casing film has a total freeshrink of from about 30 to 50 percent (L+T) at 185° F. For a butt sealbackseamed casing, the butt seal tape film can be either aheat-shrinkable film or a non-heat-shrinkable film.

As used herein, the term “sealed” refers to any and all means of closinga package, such as heat sealing via hot air and/or heated bar,ultrasonic, radio frequency sealing, and even the use of clips on, forexample, a shirred casing, etc. As used herein, the phrase “heat seal”refers to a seal formed by contacting the film with a hot element, e.g.,using a hot bar, hot wire, hot air, etc.

Preferably, the seal in the backseamed casing according to the presentinvention has a seal strength of at least 3 pounds per inch (as measuredon an Instron, per ASTM F88); more preferably, from about 5 to 100lb/in; still more preferably, from about 7 to 50 lb/in; yet still morepreferably, from about 10 to 30 lb/in; and yet still more preferably,from about 15 to 20 lb/in.

As used herein, the phrase “butt seal” refers to a seal formed bybutting opposing film edges together and thereafter sealing regions inthe vicinity of the abutted edges to a butt seal tape, as shown in FIG.5.

As used herein, the phrase “lap seal” refers to a seal formed by lappinga film over itself to form a package by sealing an inside surface of thefilm to an outside surface of the film, as shown in FIG. 4.

As used herein, the phrase “meat-contact layer”, refers to a layer of amultilayer film which is in direct contact with the meat-containingproduct packaged in the film. The meat-contact layer is an outer layer,in order to be in direct contact with the meat product. The meat-contactlayer is an inside layer in the sense that in the packaged meat product,the meat-contact layer is the innermost film layer in direct contactwith the food.

As used herein, the phrase “meat-contact surface” refers to a surface ofa meat-contact layer which is in direct contact with the meat in thepackage.

As used herein, the phrase “meat-adhesion”, and “adhered”, refer tomaintaining direct contact between the meat surface and the meat-contactsurface of the film, so that there is an absence of fat or a substantialamount of free moisture, e.g., juices emitted outside of the meatproduct, commonly referred to as “purge”. In general, there is anabsence of a substantial amount of free moisture if the level of freemoisture is from about 0 to 2%, based on the weight of the meat productbefore cooking. Preferably the amount of free moisture is from about 0to 1%, more preferably, 0 to 0.5%, and still preferably from 0 to 0.1percent based on the weight of the meat product before cooking.

As used herein, the phrase “cook-in” refers to the process of cooking aproduct packaged in a material capable of withstanding exposure to longand slow cooking conditions while containing the food product, forexample cooking at 57° C. to 121° C. (i.e., 135° F.-250° F.) for 2-12hours, preferably 57° C. to 95° C. (i.e., 135° F.-203° F.) for 2-12hours. Cook-in packaged foods are essentially pre-packaged, pre-cookedfoods which may be directly transferred to the consumer in this form.These types of foods may be consumed with or without warming. Cook-inpackaging materials maintain seal integrity, and in the case ofmultilayer films are delamination resistant. Cook-in films may also beheat-shrinkable under cook-in conditions so as to form a tightly fittingpackage. Cook-in films preferably have a tendency for adhesion to thefood product, thereby preventing “cook-out”, i.e., “purge”, which is thecollection of juices between the outer surface of the food product andthe meat-contact surface of the film, i.e., the surface in directcontact with the meat. Additional optional characteristics of films foruse in cook-in applications include delamination-resistance, low O₂permeability, heat-shrinkability representing about 20-50% biaxialshrinkage at about 85° C. (185° F.), and optical clarity.

As used herein, “EVOH” refers to ethylene vinyl alcohol copolymer. EVOHincludes saponified or hydrolyzed ethylene vinyl acetate copolymers, andrefers to a vinyl alcohol copolymer having an ethylene comonomer, andprepared by, for example, hydrolysis of vinyl acetate copolymers, or bychemical reactions with polyvinyl alcohol. The degree of hydrolysis ispreferably at least 50% and more preferably at least 85%.

As used herein, the term “barrier”, and the phrase “barrier layer”, asapplied to films and/or film layers, is used with reference to theability of a film or film layer to serve as a barrier to O₂.

As used herein, the term “lamination”, and the phrase “laminated film”,refer to the process, and resulting product, made by bonding togethertwo or more layers of film or other materials. Lamination can beaccomplished by joining layers with adhesives, joining with heat andpressure, corona treatment, and even spread coating and extrusioncoating. The term laminate is also inclusive of coextruded multilayerfilms comprising one or more tie layers.

As used herein, the term “oriented” refers to a polymer-containingmaterial which has been stretched at an elevated temperature (theorientation temperature), followed by being “set” in the stretchedconfiguration by cooling the material while substantially retaining thestretched dimensions. Upon subsequently heating unrestrained,unannealed, oriented polymer-containing material to its orientationtemperature, heat shrinkage is produced almost to the originalunstretched, i.e., pre-oriented dimensions. More particularly, the term“oriented”, as used herein, refers to oriented films, wherein theorientation can be produced in one or more of a variety of manners.

As used herein, the phrase “orientation ratio” refers to themultiplication product of the extent to which the plastic film materialis expanded in several directions, usually two directions perpendicularto one another. Expansion in the machine direction is herein referred toas “drawing”, whereas expansion in the transverse direction is hereinreferred to as “stretching”. The degree of orientation is also referredto as the orientation ratio, or sometimes as the “racking ratio”.

As used herein, the term “monomer” refers to a relatively simplecompound, usually containing carbon and of low molecular weight, whichcan react to form a polymer by combining with itself or with othersimilar molecules or compounds.

As used herein, the term “comonomer” refers to a monomer which iscopolymerized with at least one different monomer in a copolymerizationreaction, the result of which is a copolymer.

As used herein, the term “polymer” refers to the product of apolymerization reaction, and is inclusive of homopolymers, copolymers,terpolymers, etc. In general, the layers of a film can consistessentially of a single polymer, or can have still additional polymersblended therewith.

As used herein, the term “homopolymer” is used with reference to apolymer resulting from the polymerization of a single monomer, i.e., apolymer consisting essentially of a single type of repeating unit.

As used herein, the term “copolymer” refers to polymers formed by thepolymerization reaction of at least two different monomers. For example,the term “copolymer” includes the copolymerization reaction product ofethylene and an alpha-olefin, such as 1-hexene. However, the term“copolymer” is also inclusive of, for example, the copolymerization of amixture of ethylene, propylene, 1-hexene, and 1-octene.

As used herein, the term “polymerization” is inclusive ofhomopolymerizations, copolymerizations, terpolymerizations, etc., andincludes all types of copolymerizations such as random, graft, block,etc. In general, the polymers, in the films used in accordance with thepresent invention, can be prepared in accordance with any suitablepolymerization process, including slurry polymerization, gas phasepolymerization, and high pressure polymerization processes.

As used herein, the term “copolymerization” refers to the simultaneouspolymerization of two or more monomers.

As used herein, a copolymer identified in terms of a plurality ofmonomers, e.g., “propylene/ethylene copolymer”, refers to a copolymer inwhich either monomer copolymerizes in a higher weight or molar percent.However, the first listed monomer preferably is polymerized in a higherweight percent than the second listed monomer, and, for copolymers whichare terpolymers, quadripolymers, etc., preferably, the first monomercopolymerizes in a higher weight percent than the second monomer, andthe second monomer copolymerizes in a higher weight percent than thethird monomer, etc.

As used herein, terminology employing a “/” with respect to the chemicalidentity of a copolymer (e.g., “an ethylene/alpha-olefin copolymer”),identifies the comonomers which are copolymerized to produce thecopolymer. Such phrases as “ethylene alpha-olefin copolymer” is therespective equivalent of “ethylene/alpha-olefin copolymer.”

As used herein, the phrase “heterogeneous polymer” refers topolymerization reaction products of relatively wide variation inmolecular weight and relatively wide variation in compositiondistribution, i.e., polymers made, for example, using conventionalZiegler-Natta catalysts. Heterogeneous polymers are useful in variouslayers of the film used in the present invention. Such polymerstypically contain a relatively wide variety of chain lengths andcomonomer percentages.

As used herein, the phrase “heterogeneous catalyst” refers to a catalystsuitable for use in the polymerization of heterogeneous polymers, asdefined above. Heterogeneous catalysts are comprised of several kinds ofactive sites which differ in Lewis acidity and steric environment.Ziegler-Natta catalysts are heterogeneous catalysts. Examples ofZiegler-Natta heterogeneous systems include metal halides activated byan organometallic co-catalyst, such as titanium chloride, optionallycontaining magnesium chloride, complexed to trialkyl aluminum and may befound in patents such as U.S. Pat. No. 4,302,565, to GOEKE, et. al., andU.S. Pat. No. 4,302,566, to KAROL, et. al., both of which are herebyincorporated, in their entireties, by reference thereto.

As used herein, the phrase homogeneous polymer refers to polymerizationreaction products of relatively narrow molecular weight distribution andrelatively narrow composition distribution. Homogeneous polymers areuseful in various layers of the multilayer film used in the presentinvention. Homogeneous polymers exhibit a relatively even sequencing ofcomonomers within a chain, the mirroring of sequence distribution in allchains, and the similarity of length of all chains, and are typicallyprepared using metallocene, or other single-site type catalysis.

More particularly, homogeneous ethylene/alpha-olefin copolymers may becharacterized by one or more methods known to those of skill in the art,such as molecular weight distribution (M_(w)/M_(n)), compositiondistribution breadth index (CDBI), and narrow melting point range andsingle melt point behavior. The molecular weight distribution(M_(w)/M_(n)), also known as polydispersity, may be determined by gelpermeation chromatography. The homogeneous ethylene/alpha-olefincopolymers useful in this invention will have a (M_(w)/M_(n)) of lessthan 2.7. Preferably, the (M_(w)/M_(n)) will have a range of about 1.9to 2.5. More preferably, the (M_(w)/M_(n)) will have a range of about1.9 to 2.3. The composition distribution breadth index (CDBI) of suchhomogeneous ethylene/alpha-olefin copolymers will generally be greaterthan about 70 percent. The CDBI is defined as the weight percent of thecopolymer molecules having a comonomer content within 50 percent (i.e.,plus or minus 50%) of the median total molar comonomer content. The CDBIof linear polyethylene, which does not contain a comonomer, is definedto be 100%. The Composition Distribution Breadth Index (CDBI) isdetermined via the technique of Temperature Rising Elution Fractionation(TREF). CDBI determination clearly distinguishes the homogeneouscopolymers used in the present invention (narrow compositiondistribution as assessed by CDBI values generally above 70%) fromheterogeneous polymers such as VLDPEs available commercially whichgenerally have a broad composition distribution as assessed by CDBIvalues generally less than 55%. The CDBI of a copolymer is readilycalculated from data obtained from techniques known in the art, such as,for example, temperature rising elution fractionation as described, forexample, in Wild et. al., J. Poly. Sci. Poly. Phys. Ed., Vol. 20, p.441(1982). Preferably, the homogeneous ethylene/alpha-olefin copolymershave a CDBI greater than about 70%, i.e., a CDBI of from about 70% to99%. In general, the homogeneous ethylene/alpha-olefin copolymers in themultilayer films of the present invention also exhibit a relativelynarrow melting point range, in comparison with “heterogeneouscopolymers”, i.e., polymers having a CDBI of less than 55%. Preferably,the homogeneous ethylene/alpha-olefin copolymers exhibit an essentiallysingular melting point characteristic, with a peak melting point(T_(m)), as determined by Differential Scanning Colorimetry (DSC), offrom about 60° C. to 110° C. Preferably, the homogeneous copolymer has aDSC peak T_(m) of from about 90° C. to 110° C. As used herein, thephrase “essentially single melting point” means that at least about 80%,by weight, of the material corresponds to a single T_(m) peak at atemperature within the range of from about 60° C. to 110° C., andessentially no substantial fraction of the material has a peak meltingpoint in excess of about 115° C., as determined by DSC analysis. DSCmeasurements are made on a Perkin Elmer System 7 Thermal AnalysisSystem. Melting information reported are second melting data, i.e., thesample is heated at a programmed rate of 10° C./min. to a temperaturebelow its critical range. The sample is then reheated (2nd melting) at aprogrammed rate of 10° C./min.

A homogeneous ethylene/alpha-olefin copolymer can, in general, beprepared by the copolymerization of ethylene and any one or morealpha-olefin. Preferably, the alpha-olefin is a C₃-C₂₀ a-monoolefin,more preferably, a C₄-C₁₂ a-monoolefin, still more preferably, a C₄-C₈a-monoolefin. Still more preferably, the alpha-olefin comprises at leastone member selected from the group consisting of butene-1, hexene-1, andoctene-1, i.e., 1-butene, 1-hexene, and 1-octene, respectively. Mostpreferably, the alpha-olefin comprises octene-1, and/or a blend ofhexene-1 and butene-1.

Processes for preparing homogeneous polymers are disclosed in U.S. Pat.No. 5,206,075, U.S. Pat. No. 5,241,031, and PCT InternationalApplication WO 93/03093, each of which is hereby incorporated byreference thereto, in its entirety. Further details regarding theproduction and use of one genus of homogeneous ethylene/alpha-olefincopolymers are disclosed in U.S. Pat. No. 5,206,075, to HODGSON, Jr.;U.S. Pat. No. 5,241,031, to MEHTA; PCT International Publication NumberWO 93/03093, in the name of Exxon Chemical Company; PCT InternationalPublication Number WO 90/03414, in the name of Exxon Chemical Patents,Inc., all four of which are hereby incorporated in their entireties, byreference there. Still another genus of homogeneousethylene/alpha-olefin copolymers is disclosed in U.S. Pat. No.5,272,236, to LAI, et. al., and U.S. Pat. No. 5,278,272, to LAI, et.al., both of which are hereby incorporated in their entireties, byreference thereto.

As used herein, the term “polyolefin” refers to any polymerized olefin,which can be linear, branched, cyclic, aliphatic, aromatic, substituted,or unsubstituted. More specifically, included in the term polyolefin arehomopolymers of olefins, copolymers of olefins, copolymers of an olefinand an non-olefinic comonomer copolymerizable with the olefin, such asvinyl monomers, modified polymers thereof, and the like. Specificexamples include polypropylene homopolymers, polyethylene homopolymers,polybutene, propylene/alpha-olefin copolymers, ethylene/alpha-olefincopolymers, butene/alpha-olefin copolymers, ethylene/vinyl acetatecopolymers, ethylene/ethyl acrylate copolymers, ethylene/butyl acrylatecopolymers, ethylene/methyl acrylate copolymers, ethylene/acrylic acidcopolymers, ethylene/methacrylic acid copolymers, modified polyolefinresins, ionomer resins, polymethylpentene, etc. The modified polyolefinresins include modified polymers prepared by copolymerizing thehomopolymer of the olefin or copolymer thereof with an unsaturatedcarboxylic acid, e.g., maleic acid, fumaric acid or the like, or aderivative thereof such as the anhydride, ester or metal salt or thelike. It could also be obtained by incorporating into the olefinhomopolymer or copolymer, an unsaturated carboxylic acid, e.g., maleicacid, fumaric acid or the like, or a derivative thereof such as theanhydride, ester or metal salt or the like.

As used herein, terms identifying polymers, such as polyamide,polyester, “polyurethane”, etc., are inclusive of not only polymerscomprising repeating units derived from monomers known to polymerize toform a polymer of the named type, but are also inclusive of comonomers,derivatives, etc., which can copolymerize with monomers known topolymerize to produce the named polymer. Derivatives also includeionomers of the polymer(s). For example, the term “polyamide”encompasses both polymers comprising repeating units derived frommonomers, such as caprolactam, which polymerize to form a polyamide, aswell as copolymers derived from the copolymerization of caprolactam witha comonomer which when polymerized alone does not result in theformation of a polyamide. Furthermore, terms identifying polymers arealso inclusive of “blends” of such polymers with other polymers of adifferent type.

As used herein, the phrase “anhydride functionality” refers to any formof anhydride functionality, such as the anhydride of maleic acid,fumaric acid, etc., whether blended with one or more polymers, graftedonto a polymer, or copolymerized with a polymer, and, in general, isalso inclusive of derivatives of such functionalities, such as acids,esters, and metal salts derived therefrom.

As used herein, the phrase modified polymer, as well as more specificphrases such as “modified ethylene vinyl acetate copolymer”, and“modified polyolefin” refer to such polymers having an anhydridefunctionality, as defined immediately above, grafted thereon and/orcopolymerized therewith and/or blended therewith. Preferably, suchmodified polymers have the anhydride functionality grafted on orpolymerized therewith, as opposed to merely blended therewith.

As used herein, the phrase “anhydride-modified polymer” refers to one ormore of the following: (1) polymers obtained by copolymerizing ananhydride-containing monomer with a second, different monomer, and (2)anhydride grafted copolymers, and (3) a mixture of a polymer and ananhydride-containing compound.

As used herein, the phrase “ethylene alpha-olefin copolymer”, and“ethylene/alpha-olefin copolymer”, refer to such heterogeneous materialsas linear low density polyethylene (LLDPE), and very low and ultra lowdensity polyethylene (VLDPE and ULDPE); and homogeneous polymers such asmetallocene catalyzed polymers such as EXACT (TM) materials supplied byExxon, and TAFMER (TM) materials supplied by Mitsui PetrochemicalCorporation. These materials generally include copolymers of ethylenewith one or more comonomers selected from C₄ to C₁₀ alpha-olefins suchas butene-1 (i.e., 1-butene), hexene-1, octene-1, etc. in which themolecules of the copolymers comprise long chains with relatively fewside chain branches or cross-linked structures. This molecular structureis to be contrasted with conventional low or medium densitypolyethylenes which are more highly branched than their respectivecounterparts. LLDPE, as used herein, has a density usually in the rangeof from about 0.91 grams per cubic centimeter to about 0.94 grams percubic centimeter. Other ethylene/alpha-olefin copolymers, such as thelong chain branched homogeneous ethylene/alpha-olefin copolymersavailable from the Dow Chemical Company, known as AFFINITY (TM) resins,are also included as another type of ethylene alpha-olefin copolymeruseful in the present invention.

In general, the ethylene/alpha-olefin copolymer comprises a copolymerresulting from the copolymerization of from about 80 to 99 weightpercent ethylene and from 1 to 20 weight percent alpha-olefin.Preferably, the ethylene alpha-olefin copolymer comprises a copolymerresulting from the copolymerization of from about 85 to 95 weightpercent ethylene and from 5 to 15 weight percent alpha-olefin.

As used herein, the phrases “inner layer” and “internal layer” refer toany layer, of a multilayer film, having both of its principal surfacesdirectly adhered to another layer of the film.

As used herein, the phrase “outer layer” refers to any film layer of amultilayer film having only one of its principal surfaces directlyadhered to another layer of the film.

As used herein, the phrase “inside layer” refers to the outer layer, ofa multilayer film packaging a product, which is closest to the product,relative to the other layers of the multilayer film.

As used herein, the phrase “outside layer” refers to the outer layer, ofa multilayer film packaging a product, which is furthest from theproduct relative to the other layers of the multilayer film.

As used herein, the phrase “directly adhered”, as applied to filmlayers, is defined as adhesion of the subject film layer to the objectfilm layer, without a tie layer, adhesive, or other layer therebetween.In contrast, as used herein, the word “between”, as applied to a filmlayer expressed as being between two other specified layers, includesboth direct adherence of the subject layer between to the two otherlayers it is between, as well as including a lack of direct adherence toeither or both of the two other layers the subject layer is between,i.e., one or more additional layers can be imposed between the subjectlayer and one or more of the layers the subject layer is between.

As used herein, the term “core”, and the phrase “core layer”, as appliedto multilayer films, refer to any internal film layer which has aprimary function other than serving as an adhesive or compatibilizer foradhering two layers to one another. Usually, the core layer or layersprovide the multilayer film with a desired level of strength, e.g.,modulus, and/or optics, and/or added abuse resistance, and/or specificimpermeability.

As used herein, the phrases “seal layer” and “sealant layer”, withrespect to multilayer films, refers to an outer film layer, or layers,involved in the sealing of the film to itself or another layer. Itshould also be recognized that in general, the outer 0.5 to 3 mils of afilm can be involved in the sealing of the film to itself or anotherlayer. With respect to packages having only fin-type seals, as opposedto lap seals, the phrase “sealant layer” generally refers to the insidefilm layer of a package, as well as supporting layers adjacent thissealant layer often being sealed to itself, and frequently serving as afood contact layer in the packaging of foods.

As used herein, the phrase “tie layer” refers to any internal layerhaving the primary purpose of adhering two layers to one another.

As used herein, the phrase “skin layer” refers to an outside layer of amultilayer film in packaging a product, this skin layer being subject toabuse.

As used herein, the phrase “bulk layer” refers to any layer of a filmwhich is present for the purpose of increasing the abuse-resistance,toughness, modulus, etc., of a multilayer film. Bulk layers generallycomprise polymers which are inexpensive relative to other polymers inthe film which provide some specific purpose unrelated toabuse-resistance, modulus, etc.

As used herein, the term “extrusion” is used with reference to theprocess of forming continuous shapes by forcing a molten plasticmaterial through a die, followed by cooling or chemical hardening.Immediately prior to extrusion through the die, the relativelyhigh-viscosity polymeric material is fed into a rotating screw ofvariable pitch, which forces it through the die.

As used herein, the term “coextrusion” refers to the process ofextruding two or more materials through a single die with two or moreorifices arranged so that the extrudates merge and weld together into alaminar structure before chilling, i.e., quenching. Coextrusion can beemployed in film blowing, free film extrusion, and extrusion coatingprocesses.

As used herein, the phrase “machine direction”, herein abbreviated “MD”,refers to a direction “along the length” of the film, i.e., in thedirection of the film as the film is formed during extrusion and/orcoating.

As used herein, the phrase “transverse direction”, herein abbreviated“TD”, refers to a direction across the film, perpendicular to themachine or longitudinal direction.

As used herein, the phrase “free shrink” refers to the percentdimensional change in a 10 cm×10 cm specimen of film, when subjected toselected heat, as measured by ASTM D 2732, as known to those of skill inthe art.

According to the first aspect of the present invention as set forthabove, if the first polyolefin comprises ethylene/unsaturated acid,propylene/unsaturated acid, and/or butene/unsaturated acid, preferablythe unsaturated acid mer is present in an amount of from about 4 to 30weight percent, based on the weight of the copolymer; more preferably,from about 7 to 20 percent; still more preferably, from about 8 to 15percent; and, yet still more preferably, from about 9 to 13 percent.Depending upon the meat product, if the unsaturated acid mer is presentin an amount less than 6 weight percent, sufficient purge-resistance maynot be achieved upon cooking the meat product in the casing. On theother hand, if the amount of unsaturated acid mer is present in anamount greater than about 20 weight percent, the softening point of theunsaturated acid copolymer may be too low to facilitate film productionand/or obtain satisfactory seal strength for cook-in end use. Thus, theoptimal level of unsaturated acid mer depends on the manner in which thefilm is produced, and the particular end-use of the film, e.g., the typeof meat being packaged, and the cook-in conditions.

If the first polyolefin comprises anhydride-containing polyolefincomprising an anhydride-functionality, preferably the anhydridefunctionality is present in an amount of from about 1 to 10 weightpercent, based on the weight of the anhydride-containing polyolefin;more preferably, from about 2 to 5 weight percent.

In a lap-sealed backseamed casing according the present invention,preferably the first polyolefin has a vicat softening point of at least70° C., more preferably at least 80° C., and still more preferably atleast 90° C., in order to provide a desired level of seal strength.However, in a butt-sealed backseamed casing according to the presentinvention, in which a butt-tape film is sealed to the outer surface ofthe third film layer, the lower-limit of the softening point of thefirst polyolefin may be less critical.

Preferably, the first polyolefin is present in the first outer layer inan amount of from about 10 to 50 weight percent, based on the weight ofthe first layer; more preferably, in an amount of from about 10 to 30percent; and still more preferably, in an amount of from about 15 to 25percent.

As the third polyolefin, LLDPE is more preferred than propylene/ethylenecopolymer because LLDPE produces a seal having less “pucker”, if thesecond polyolefin also comprises LLDPE and the casing is a lap-sealbackseamed casing. The third polyolefin provides the first layer with ahigh melting point resin, which is advantageous for cook-in end use,where the casing is subjected to relatively high temperatures for arelatively long period of time. Preferably, the third polyolefin has amelting point less than 160° C.; more preferably, less than 140° C., andstill more preferably, less than 130° C. Preferably, the thirdpolyolefin has a vicat softening point of at least 80° C., morepreferably, at least 90° C., and still more preferably, at least 100° C.

In the second layer, the first polyamide preferably comprises at leastone member selected from the group consisting of polyamide 6, polyamide66, polyamide 9, polyamide 10, polyamide 11, polyamide 12, polyamide 69,polyamide 610, polyamide 612, polyamide 6I, polyamide 6T, and copolymersthereof; more preferably, at least one member selected from the groupconsisting of polyamide 6, polyamide 66 and polyamide 6/66. Preferably,the first polyamide has a melting point of at least 350° F.; morepreferably, at least 370° F.; still more preferably, at least 390° F.

Preferably, the second layer further comprises a third polyamide havinga melting point of less than about 350° F. Preferably, the second layercomprises: (a) polyamide 6 in an amount of from about 40 to 90 weightpercent, based on the weight of the second layer; and (b) copolyamide6/12 in an amount of from about 10 to 60 weight percent, based on theweight of the second layer, wherein the copolyamide 6/12 comprisescaprolactam mer in an amount of from about 30 to 70 weight percent (morepreferably, 40 to 60 weight percent). Preferably, the first polyamidehas a melting point above 350° F., and the third polyamide has a meltingpoint below 350° F., as this combination has been found to produce acombination of modulus, orientability, seal strength, andpinhole-resistance which is preferred.

Preferably, the second polyolefin comprises at least one member selectedfrom the group consisting of polyethylene homopolymer, polyethylenecopolymer, polypropylene homopolymer, polypropylene copolymer,polybutene homopolymer, and polybutene copolymer. More preferably, thesecond polyolefin comprises at least one member selected from the groupconsisting of ethylene/alpha-olefin copolymer, propylene/alpha-olefincopolymer, butene/alpha-olefin copolymer, ethylene/unsaturated estercopolymer, and ethylene/unsaturated acid copolymer. Still morepreferably, the second polyolefin comprises at least one member selectedfrom the group consisting of linear low density polyethylene (LLDPE),propylene/ethylene copolymer, and propylene/butene copolymer. Yet stillmore preferably, the second polyolefin comprises LLDPE. In a lap-sealbackseam casing according to the present invention, preferably thesecond polyolefin and the third polyolefin are the same polymer.

If the fifth and sixth layers each comprise polystyrene or polyurethane,they may be the same polystyrene and/or polyurethane, or differentpolystyrenes and/or polyurethanes. In serving as tie layers, preferablythe fifth and sixth layers each assist the adhesion of the preferablypolyolefinic first and third layers to the polyamide layer, as well asto the O₂-barrier layer, if present.

The butt-seal tape film is chosen so that it is seal-compatible with thesealant surface of the casing film. Preferably, the butt-seal tape filmcomprises polyolefin as an outer sealing layer. More preferably, thebutt-seal tape film further comprises an O₂-barrier layer. Still morepreferably, the butt-seal tape film further comprises two tie layers,i.e., a tie layer between the O₂-barrier layer and each of the two outerlayers, each of which comprise polyolefin. Preferably, the butt-sealtape film is heat-shrinkable, and preferably, the butt-seal tape filmcomprises an outer sealing layer comprising polyolefin having a meltingpoint of from about 90° C.-150° C.; more preferably, from about 100°C.-130° C.

The seal layer of the butt-seal tape film is an outer film layer whichpreferably comprises at least one member selected from the groupconsisting of polyethylene homopolymer, polyethylene copolymer,polypropylene homopolymer, polypropylene copolymer, polybutenehomopolymer, and polybutene copolymer; more preferably,ethylene/alpha-olefin copolymer, propylene/alpha-olefin copolymer,butene/alpha-olefin copolymer, ethylene/unsaturated ester copolymer, andethylene/unsaturated acid copolymer; still more preferably, linear lowdensity polyethylene (LLDPE), propylene/ethylene copolymer, andpropylene/butene copolymer.

In the casing film according to the third aspect of the presentinvention, all of the various polymers present in each of the filmlayers are preferably as described above according to the first aspectof the present invention, except that the first polyolefin of the firstlayer has surface energy of less than 34 dynes/cm, more preferably, lessthan 32 dynes/cm. Thus, in the third aspect of the present invention,the first polyolefin preferably comprises at least one member selectedfrom the group consisting of polyethylene homopolymer, polyethylenecopolymer, polypropylene homopolymer, polypropylene copolymer,polybutene homopolymer, and polybutene copolymer. More preferably, thefirst polyolefin comprises at least one member selected from the groupconsisting of ethylene/alpha-olefin copolymer, propylene/alpha-olefincopolymer, butene/alpha-olefin copolymer, ethylene/unsaturated acidcopolymer, and ethylene/unsaturated ester copolymer. Still morepreferably, the first polyolefin comprises at least one member selectedfrom the group consisting of linear low density polyethylene (LLDPE),propylene/ethylene copolymer, and propylene/butene copolymer. Yet stillmore preferably, the first polyolefin comprises LLDPE.

Preferably, the multilayer film has a shrink tension of at least about10 psi, more preferably, from about 20-1000 psi, still more preferably,from about 100 to 600 psi; and yet still more preferably, from about 300to 500 psi.

A preferred backseamed casing according to the present inventioncomprises a multilayer heat shrinkable film comprising a meat-adhesionlayer comprising a polar polymer, which provides a high level of meatadhesion, especially to intermediate/high protein-containing meatproducts. Although this film can be corona treated, the film of theinvention does not require corona treatment in order to exhibit adesired level of meat adhesion with products such as turkey,good-to-intermediate quality ham, and roast beef. However, thebackseamed casing film of the present invention can be corona treated inorder to provide an enhanced level of adhesion, especially with high fatproducts. Typically, films which by themselves have a relatively lowlevel of meat-adhesion exhibit the ‘buffing-off’ problem describedabove, at least at the backseamed edges thereof. However, the films ofthe present invention have an advantage in that respect. Because theuntreated films already have an acceptable level of meat-adhesion tointermediate-quality meat products, even when the corona treatment isbuffed-off the surface during the backseaming operation, there issufficient protein-adhesion from the polymer to prevent purge orfatting-out. Thus, the ultimate package still has an acceptable level ofadhesion. Optionally, corona treatment could also be carried out afterthe backseamed tubing is made. Here, too, if a relativelylow-meat-adhering-polymer is used as the inside casing layer and theresulting backseamed tubing is then corona treated, substantial purge(also known as cook-out and fatting-out) can occur on a strip at theedge of the backseamed tubing, where there is insufficient coronatreatment (inherent in the process used to internally corona treat).However, the corona treatment of a film surface which already has anenhanced level of meat-adhesion (as is the case in the presentinvention) reduces or eliminates the purge or cook-loss at the casinglay flat edges (which, as described above, have not been substantiallytreated). Thus, the backseamed casing of the present invention avoidsthe “buffing off problem” associated with corona treatment, while at thesame time achieving a satisfactory level of meat adhesion to variousdifferent kinds of protein-containing meat products.

As described above, the second layer of the casing film must have athickness of at least about 5% of a total thickness of theheat-shrinkable casing film. That is, if the thickness of the secondlayer is less than about 5 percent of the total thickness of the film,the second layer may not perform adequately in preventing the film fromshrinking down against the forming shoe.

If the heat-shrinkable casing film in the backseamed casing is made byorienting a tape which is heated over a very short time period, such asa tape heated by infrared radiation, the thickness of the second layercould be as high as 70%, based on the thickness of the multilayer film.However, if the film is heated over a relatively long time period, suchas being heated in hot water, the preferred polyamides tend tocrystallize to a relatively high level before the orientation step,which produces problems during the orientation step (the rate ofcrystallization depends on the type of polyamide used). In this lattersituation, typically, the greater the thickness of the second layer, themore difficult it is to orient to obtain the resulting casing film. Thisforces a practical limit on the maximum percentage thickness of thesecond layer (especially when the most preferred polyamides are used),based on the total thickness of the multilayer casing film. Thus, ifhot-water is used as the orientation medium, the second layer of thecasing film preferably has a thickness of from about 5 to 50 percent ofthe total thickness of the casing film; more preferably, from about 5 to40 percent; still more preferably, from about 10 to 30 percent; and yetstill more preferably, from about 10 to 20 percent, based on a totalthickness of the multi-layer film.

It has been discovered that the second layer, which preferably comprisespolyamide, serves to prevent necking down on the forming shoe during thebackseaming process. Necking down typically occurs during thebackseaming process when the film is drawn so tightly around the formingshoe (as a result of the film shrinking due to the heat generatedoutwards from the seal area during the backseaming process) that itcannot be forwarded. The presence of the second layer, significantlyreduces the necking down of the film by reducing that region of the filmwhich shrinks due to the propagation of heat outward from the heat sealbar.

Preferably, the backseamed casing of the present invention comprises acasing film having from 3 to 20 layers; more preferably, from 4 to 12layers; still more preferably, from 6 to 10 layers.

Preferably, the multilayer casing film used in the backseamed casingaccording to the present invention can have any total thickness desired,so long as the film provides the desired properties for the particularpackaging operation in which the film is used. Preferably, the casingfilm used in the present invention has a total thickness, i.e., acombined thickness of all layers, of from about 0.5 to 10 mils (1 milequals 0.001 inch); more preferably, from about 1 to 8 mils; and stillmore preferably, from 2 to 4 mils.

It should be noted that the modulus of the casing film should be highenough that so that the film does not stretch to an undesirable degreeduring the backseaming process. Preferably, the casing film has amodulus of at least 20,000 psi; more preferably, from about 30,000 to250,000 psi; still more preferably, from about 40,000 to 150,000 psi.;yet still more preferably, from about 45,000 to 120,000; and even yetstill more preferably, from about 50,000 to 70,000 psi. It should bekept in mind that if the modulus of the casing film is too high,problems could occur after backseaming, e.g., the film could flex-crackwhen being wound up after backseaming or cause difficulty in tracking.Furthermore, too high a modulus is especially undesirable if the film isto be used as a casing which is to undergo shirring, as films of toohigh a modulus may flex-crack during shirring. On the other hand, if themodulus of the film is too low, the film tends to stretch too muchduring backseaming, thereby producing backseamed casing of low qualityin that it does not backseam acceptably, has a wavy appearance, and/orhas ruffled edges, and/or seal pucker, and/or does not track wellthrough the machine.

FIG. 1 illustrates lap-seal backseamed casing 11 according to thepresent invention. Lap-seal backseamed casing 11 comprisesheat-shrinkable casing film 12, which is sealed to itself at backseamlap-seal 13.

FIG. 2 illustrates an enlarged cross-sectional view of heat-shrinkablecasing film 12, which is especially suited to the packaging of meat. InFIG. 2, casing film 12 comprises: first layer 14, second layer 16, thirdlayer 18, fourth layer 20, fifth layer 22, sixth layer 24, seventh layer26, and eighth layer 28.

First layer 14 is an outer film layer which serves as an inside layer ofthe casing film. First layer 14 has outer meat-contact surface 15 fordirect contact, and adhesion to, the meat being packaged in casing 11.Preferably, first layer 14 has a thickness of from about 0.1 to 3 mils;more preferably, from 0.2 to 1 mil; still more preferably, from 0.3 to0.8 mil; and yet still more preferably, about 0.5 mils. First layer 14comprises a polar polymer which preferably has a surface energy greaterthan 32 dynes/cm, more preferably greater than 34 dynes/cm, and stillmore preferably greater than 36 dynes/cm. Preferably, first layer 14comprises a first polyolefin comprising at least one member selectedfrom the group consisting of:

(i) ethylene/unsaturated acid copolymer, propylene/unsaturated acidcopolymer, and butene/unsaturated acid copolymer, wherein theunsaturated acid (mer) is present in an amount of at least 4 weightpercent, based on the weight of the copolymer; and

(ii) anhydride-containing polyolefin comprising ananhydride-functionality, wherein the anhydride functionality is presentin an amount of at least 1 weight percent, based on the weight of theanhydride-containing polyolefin;

More preferably, first layer 14 comprises a first polyolefin comprisingat least one member selected from the group consisting of:

(i) ethylene/unsaturated acid copolymer, propylene/unsaturated acidcopolymer, and butene/unsaturated acid copolymer, wherein theunsaturated acid (mer) is present in an amount of from about 6-30%, morepreferably from about 7-20%, still more preferably from about 8-15%, andyet still more preferably, from about 9-13%, based on the weight of thecopolymer; and

(ii) anhydride-containing polyolefin comprising ananhydride-functionality, wherein the anhydride functionality is presentin an amount of from about 1 to 10 weight percent, based on the weightof the anhydride-containing polyolefin; more preferably from about 2 to5 weight percent.

If the first polyolefin comprises unsaturated acid copolymer, if theunsaturated acid mer is present in an amount less than 6 weight percent,sufficient purge resistance may not be achieved. On the other hand, ifthe amount of unsaturated acid (mer) in the copolymer is greater thanabout 20 weight percent, the softening point of the unsaturated acidcopolymer may be too low to facilitate processing into film and/orobtain satisfactory seal strength during cooking. The preferredunsaturated acid (mer) level may vary depending on the end application,i.e., the type of meat product to be adhered to.

In any backseamed casing according to the present invention, preferably,the inside film layer (which serves as a food-contact layer, and, in thelap seal backseamed casing according to the present invention alsoserves as a sealant layer) does not comprise a blend ofpropylene/ethylene copolymer and homogeneous ethylene/alpha-olefincopolymer having a density of less than 0.90. That is, if this blendmakes up the majority of the seal layer, the seal strength may be lessthan preferred. Furthermore, if this blend makes up the majority of theseal layer, no core layer of polyester and/or first polyamide isrequired in order to backseam the film without a detrimental degree ofnecking down on the forming shoe.

Multilayer film 12 may be used in either a lap-seal backseamed casing ora butt-seal backseamed casing. In a lap-seal backseamed casing such ascasing 11, preferably the first polyolefin has a vicat softening pointof at least 70° C., more preferably at least 80° C., in order to retaingood seal strength during cook-in. However, for a butt-sealed backseamedcasing, the lower-limit of the softening point of the first polyolefinmay be less critical, as it is both the softening point of the thirdlayer of the casing film, as well as the softening point of the sealantlayer of the butt-seal tape film, which govern sealability and sealstrength during cooking.

Preferably, first layer 14 further comprises a third polyolefincomprising at least one member selected from the group consisting ofpolyethylene homopolymer, polyethylene copolymer, polypropylenehomopolymer, polypropylene copolymer, polybutene homopolymer, andpolybutene copolymer. More preferably, the third polyolefin comprises atleast one member selected from the group consisting ofethylene/alpha-olefin copolymer, propylene/alpha-olefin copolymer,butene/alpha-olefin copolymer, ethylene/unsaturated acid copolymer, andethylene/unsaturated ester copolymer. Even more preferably, the thirdpolyolefin comprises at least one member selected from the groupconsisting of linear low density polyethylene (LLDPE),propylene/ethylene copolymer, and propylene/butene copolymer.Preferably, the third polyolefin has a vicat softening point of at least80° C., more preferably, at least 90° C., and even more preferably atleast 100° C. Preferably, the first polyolefin is present in an amountof from about 10-50%, more preferably, in an amount of from about10-30%, and even more preferably, in an amount of from about 15-25%,based on the composition of the first outer layer.

The third polyolefin provides first layer 14 with a higher softeningpoint polymer to enhance the stability of the film, and seals thereof,during cook-in. Furthermore, the dilution of the polar polymer with arelatively non-polar polymer, i.e., the third polyolefin, does notsignificantly decrease the purge-resistance characteristics of the firstlayer of the casing film. Preferably, first layer 14 comprises a blendof 80 weight percent LLDPE and 20 weight percent ethylene/unsaturatedacid copolymer.

Second layer 16 is an inner film layer which is between first layer 14and third layer 18. Second layer 16 provides casing film 11 with thecharacteristic of undergoing the backseaming operation without neckingdown on the forming shoe. Second layer 16 also helps to provide a betterquality casing film by making casing film 12 easier to orient, andfacilitating faster backseaming speeds, and also imparting enhanced sealstrength, toughness, pin-hole resistance and elastic recovery to casingfilm 12. Second layer 16 preferably comprises at least one memberselected from the group consisting of polyester, and first polyamide,i.e., polymers having relatively high modulus and/or relatively highelastic recovery. More preferably, second layer 16 comprises the firstpolyamide; still more preferably, at least one member selected from thegroup consisting of polyamide 6, polyamide 66, polyamide 9, polyamide10, polyamide 11, polyamide 12, polyamide 69, polyamide 610, polyamide612, polyamide 6I, polyamide 6T, as well as copolymers prepared fromcopolymerization of any one or more of the monomers used in thepreparation of any of these polyamides; and yet still more preferably,at least one member selected from the group consisting of polyamide 6,polyamide 66 and polyamide 6/66. Preferably, the first polyamide has amelting point of at least 350° F.; more preferably, at least 370° F.;even more preferably, at least 390° F. Preferably, second layer 16 has athickness of from about 0.05 to 1 mil; preferably, from 0.1 to 0.5 mil;more preferably, from about 0.2 to 0.4 mil, and still more preferably,about 0.3 mils.

Preferably, second layer 16 further comprises a third polyamide having amelting point of less than about 350° F. Preferably, second layer 16comprises: (a) polyamide 6 in an amount of from about 40 to 90 weightpercent, based on the weight of the first inner layer; and (b)copolyamide 6/12 in an amount of from about 10 to 60 weight percent,based on the weight of the first inner layer, wherein the copolyamide6/12 comprises caprolactam (mer) in an amount of from about 30 to 70weight percent, based on the weight of the copolyamide; more preferably,from about 40 to 60 weight percent.

Third layer 18 is an outer film layer which serves as an outsideabuse-resistant and heat-seal layer of casing 11. Preferably, thirdlayer 18 has a thickness of from about 0.1 to 3 mils; more preferably,from about 0.2 to 1 mil; still more preferably, from about 0.3 to 0.8mil; and, yet still more preferably, about 0.35 to 0.65 mil.

Preferably, third layer 18 comprises at least one member selected fromthe group consisting of second polyolefin, polystyrene, secondpolyamide, polyester, polymerized ethylene/vinyl alcohol copolymer,polyvinylidene chloride, polyether, polyurethane, polycarbonate, andstarch-containing polymer; more preferably, third layer 18 comprises thesecond polyolefin; still more preferably, at least one member selectedfrom the group consisting of polyethylene homopolymer, polyethylenecopolymer, polypropylene homopolymer, polypropylene copolymer,polybutene homopolymer, and polybutene copolymer; yet still morepreferably, third layer 18 comprises at least one member selected fromthe group consisting of ethylene/alpha-olefin copolymer,propylene/alpha-olefin copolymer, butene/alpha-olefin copolymer,ethylene/unsaturated ester copolymer, and ethylene/unsaturated acidcopolymer; and yet still even more preferably, third layer 18 comprisesat least one member selected from the group consisting of linear lowdensity polyethylene (LLDPE), propylene/ethylene copolymer, andpropylene/butene copolymer.

In a lap-seal backseam casing, the second polyolefin and the thirdpolyolefin are preferably the same polymer.

Preferably, the second polyolefin has a vicat softening point of atleast 80° C., more preferably, at least 90° C., and even more preferablyat least 100° C. The softening point of the second polyolefin needs tobe high enough for the casing to survive cook-in.

Fourth layer 20 is an internal layer which is between first layer 14 andthird layer 18, and preferably comprises a polymer having relativelyhigh oxygen barrier characteristics. Preferably, fourth layer 20 has athickness of from about 0.05 to 2 mils; more preferably, from 0.05 to0.5 mil; still more preferably, from 0.1 to 0.3 mil; and yet still morepreferably, from about 0.12 to 0.17 mils. In general, fourth layer 20comprises at least one member selected from the group consisting ofpolymerized ethylene vinyl alcohol (EVOH), polyvinylidene chloride,fourth polyamide, polyalkylene carbonate, and polyester; preferably, atleast one member selected from the group consisting of polymerizedethylene vinyl alcohol and fourth polyamide; more preferably,polymerized ethylene vinyl alcohol; still more preferably, polymerizedethylene vinyl alcohol having about 44 mole percent ethylene.

Fifth layer 22 and sixth layer 24 are tie layers in casing film 12.Fifth layer 22 is between first layer 14 and second layer 16; sixthlayer 24 is between second layer 16 and third layer 18. As a generalrule, tie layers should have a relatively high degree of compatibilitywith barrier layers, such as polymerized EVOH, or the polyamide layer,as well as non-barrier layers, such as polymerized ethylene alpha-olefincopolymer. The composition, number, and thickness of tie layers is asknown to those of skill in the art. Preferably, fifth layer 22 and sixthlayer 24 each have a thickness of from about 0.05 to 2 mils; morepreferably, from about 0.05 to 0.5 mil; still more preferably, fromabout 0.1 to 0.3 mil; and yet still more preferably, from about 0.12 to0.17 mils. Preferably, fifth layer 22 comprises at least one memberselected from the group consisting of fourth polyolefin, polystyrene andpolyurethane; more preferably, at least one member selected from thegroup consisting of modified ethylene/alpha-olefin copolymer, modifiedethylene/unsaturated ester copolymer, and modified ethylene/unsaturatedacid copolymer. Preferably, sixth layer 24 comprises at least one memberselected from the group consisting of fifth polyolefin, polystyrene andpolyurethane; more preferably, at least one member selected from thegroup consisting of modified ethylene/alpha-olefin copolymer, modifiedethylene/unsaturated ester copolymer, and modified ethylene/unsaturatedacid copolymer.

Seventh layer 26 is a core layer between first layer 14 and second layer16. Seventh layer 26 provides the multilayer casing film 12 film withdesired abuse, shrink, and optical characteristics, and preferablycomprises a polymer having relatively low cost while providing thesecharacteristics. Preferably, seventh layer 26 has a thickness of fromabout 0.1 to 3 mils; more preferably, from 0.2 to 1.5 mils; still morepreferably, from 0.3 to 1 mil; and yet still more preferably, from about0.50 to 0.80 mils. Preferably, seventh layer 26 comprises at least onemember selected from the group consisting of polyolefin, polyamide,polyester, and polyurethane; more preferably, polyolefin; still morepreferably, at least one member selected from the group consisting ofethylene/alpha-olefin copolymer, propylene/alpha-olefin copolymer,butene/alpha-olefin copolymer, ethylene/unsaturated ester copolymer, andethylene/unsaturated acid copolymer; and yet still more preferably, ablend of 80 weight percent ethylene vinyl acetate copolymer (having 6weight percent vinyl acetate mer) with 20 weight percent high densitypolyethylene.

Eighth layer 28 is a core layer between second layer 16 and third layer18. Eighth layer 18 also provides the multilayer film with desiredabuse, shrink, and optical characteristics, and preferably comprises apolymer having relatively low cost while providing these attributes. Ingeneral, eighth layer 18 can have a thickness of from about 0.1 to 3mils; preferably, from 0.2 to 1.5 mil; more preferably, from 0.3 to 1mil; and still more preferably, from about 0.50 to 0.80 mils. Ingeneral, eighth layer 18 comprises at least one member selected from thegroup consisting of polyolefin, polyamide, polyester, and polyurethane;preferably, polyolefin; more preferably at least one member selectedfrom the group consisting of ethylene/alpha-olefin copolymer,propylene/alpha-olefin copolymer, butene/alpha-olefin copolymer,ethylene/unsaturated ester copolymer, and ethylene/unsaturated acidcopolymer; still more preferably, a blend of 80 weight percent ethylenevinyl acetate copolymer (having 6 weight percent vinyl acetate) with 20weight percent ethylene/unsaturated acid copolymer.

Seventh layer 26 and eighth layer 28 are typically chosen in compositionand layer thickness so as to provide a relatively flat, curl-free,heat-shrinkable casing film. Preferably, seventh layer 26 and eighthlayer 28 have a composition and thickness so as to provide themultilayer film with as much cross-sectional symmetry as possible.Cross-sectional symmetry provides the film with the desiredcharacteristics of low curl and low floppiness.

If “a” represents a sum of the thicknesses of the first, fifth, andseventh layers, and “b” represents a sum of the thicknesses of thesecond, sixth, and eighth layers, then preferably, a:b is from about0.5:1 to 1.5:1, more preferably 0.7:1 to 1.3:1, still more preferably,from about 0.8:1 to 1.2:1.

In casing 11, backseam seal 13 can be formed using any one or more of awide variety of sealing devices, as known to those of skill in the art,such as heat sealing via hot air and/or heated bar and/or hot wire,ultrasonic sealing, radio frequency sealing, etc. However, a preferredsealing mechanism is the use of a heated seal bar which provides forbetter sealability and can provide better ultimate seal strength, thusproviding seals capable of surviving the cooking process.

FIG. 3 illustrates alternative preferred six-layer, heat-shrinkablecasing film 30 suitable for use as a lap-seal casing as illustrated inFIG. 1, as well as a butt-seal casing as illustrated in FIG. 5. As withmultilayer film 12 of FIG. 2, multilayer film 30 is also especiallysuited to the packaging of meat products which are thereafter subjectedto cook-in. Casing film 30 comprises first layer 32, second layer 34,third layer 36, fourth layer 38, fifth layer 40, and sixth layer 42.

First layer 32 is an outer film layer which serves as an inside casingfilm layer, and accordingly is a meat-contact layer which is analogousto first layer 14 of FIG. 2. When in the form of casing, first layer 32has inside meat-contact surface 33 for direct contact with, and adhesionto, the meat within the casing. If casing film 30 is used to makelap-seal casing 11 as illustrated in FIG. 1, first layer 32 is sealed tosecond layer 34 at backseam lap seal 13, this seal being located where aportion of outer surface 33 overlaps outside surface 35 of casing film30. First layer 32 has the same general and preferred thickness andchemical composition as first layer 14 of FIG. 2. However, first layer32 most preferably has a thickness of 0.8 mils.

Second layer 34 is a core layer between first layer 32 and third layer36, and in general is analogous to second layer 16 of FIG. 2. Secondlayer 34 has the same general and preferred thickness and chemicalcomposition as second layer 16 of FIG. 2.

Third film layer 36 is an outer film layer which serves as an outside,abuse-resistant heat-seal layer of casing 11. Preferably, third layer 36is analogous to third layer 18 of FIG. 1. Third layer 36 has the samegeneral and preferred thickness and chemical composition as third layer18 of FIG. 1. However, third layer 36 most preferably has a thickness ofabout 0.8 mils.

Fourth layer 38 is an inner layer between first layer 32 and third layer36, and in general is analogous to fourth layer 20 of FIG. 2. Fourthlayer 38 has the same general and preferred thickness and chemicalcomposition as fourth layer 20 of FIG. 2.

Fifth layer 40 is a tie layer between first layer 32 and second layer34, and in general is analogous to fifth layer 22 of FIG. 2. Fifth layer40 has the same general and preferred thickness and chemical compositionas fifth layer 22 of FIG. 2.

Sixth layer 42 is a tie layer between second layer 34 and third layer36, and in general is analogous to sixth layer 24 of FIG. 2. Sixth layer42 has the same general and preferred thickness and chemical compositionas sixth layer 24 of FIG. 2.

FIG. 4 illustrates an alternative preferred three-layer,heat-shrinkable, multi-layer casing film 44 suitable for use as alap-seal casing 11 as illustrated in FIG. 1. As with multilayer film 12of FIG. 2, multi-layer film 44 is also especially suited to thepackaging of meat products which are thereafter subjected to cook-in.Casing film 44 comprises first layer 46, second layer 48, and thirdlayer 50.

First layer 46 is an outer film layer which serves as an inside casingfilm layer, and is a meat-contact layer which is analogous to firstlayer 14 of FIG. 2. When in the form of a casing, first layer 46 ofmultilayer film 44 has inside meat-contact surface 47 for direct contactwith, and adhesion to, the meat within the casing. If casing film 44 isused to make lap-seal casing 11 as illustrated in FIG. 1, first layer 46is sealed to third layer 50 at backseam lap seal 13, this seal beinglocated where a portion of inside surface 47 overlaps a portion ofoutside surface 51 of casing film 44. Preferably, first layer 46 has thesame thickness and chemical composition as first layer 14 of FIG. 2;more preferably, first layer 46 comprises a modified polyolefin forimproved bonding to second layer 48; still more preferably, first layer46 comprises anhydride-modified LLDPE as the third polyolefin. Also,more preferably, first layer 46 has a thickness of 1.0 mil.

Second layer 48 is a core layer between first layer 46 and third layer50, and in general is analogous to second layer 16 of FIG. 2. Secondlayer 48 has the same general and preferred thickness and chemicalcomposition as second layer 16 of FIG. 2.

Third layer 50 is an outer abuse-resistant layer and heat-seal layer,which is analogous to third layer 18 of FIG. 2. Preferably, third layer50 has the same thickness and chemical composition as third layer 18 ofFIG. 2. However, third layer 50 further comprises a modified polyolefinfor improved bonding to second layer 48; more preferably, third layer 50comprises, as the second polyolefin, 100 weight percentanhydride-modified LLDPE. Also, more preferably, third layer 50 has athickness of 1.0 mil.

FIG. 5 illustrates a cross-sectional view of butt-seal backseamed casing52, in accordance with the present invention. Butt-seal backseamedcasing 52 comprises heat-shrinkable casing film 54 having abuttinglongitudinal edges 56 and 58, and butt-seal tape 60, one side of whichis sealed to outside surface 55 of casing film 54, seals 59 and 61 beingin regions adjacent to and along longitudinal edges 56 and 58. In thismanner, a tubular casing is provided in which a product can be packaged,especially a meat product which is thereafter subjected to cook-in whilepackaged in butt-seal backseamed casing 52.

FIG. 6 illustrates preferred heat-shrinkable, multilayer film 62 for useas casing film 54 in butt-seal backseamed casing 52 illustrated in FIG.5. Multilayer film 62 comprises first layer 64, second layer 66, thirdlayer 68, fourth layer 70, fifth layer 72, and sixth layer 74.

First film layer 64 is a meat-contact and meat adhesion which isanalogous to first layer 32 of the film of FIG. 3. First film layer 64serves as an inside casing layer, and provides meat-contact surface 65for direct contact with, and adhesion to, meat packaged in the casingwhich is thereafter subjected to cook-in. Preferably, first layer 64 hasthe same thickness and chemical composition as first layer 32 of FIG. 3.

Second layer 66 is an inner film layer which serves as a casing corelayer which reduces or eliminates necking down on the forming shoeduring the backseaming operation. Second layer 66 is between first layer64 and third layer 68, and is analogous to second layer 34 of the filmof FIG. 3. Preferably, second layer 66 has the same thickness andchemical composition as second layer 34.

Third layer 68 is an outer film layer which serves as an outside casingabuse-resistance and heat-seal layer, and is analogous to third layer 36of the film of FIG. 3. Preferably, third layer 68 has the same thicknessand chemical composition as third layer 36.

Fourth layer 70 is an inner film layer which serves as an O₂-barrierlayer, is between first film layer 64 and third film layer 68, and isanalogous to fourth layer 38 in film 30 of FIG. 3. Preferably, fourthlayer 70 has the same thickness and chemical composition as fourth layer38.

Fifth layer 72 is an inner film layer which serves as a tie layer, andis between first film layer 64 and second film layer 66, and isanalogous to fifth layer 40 in film 30 of FIG. 3. Preferably, fifthlayer 72 has the same thickness and chemical composition as fifth layer40.

Sixth layer 74 is an inner film layer which serves as a tie layer, andis between second film layer 66 and third film layer 68, and isanalogous to sixth layer 42 in film 30 of FIG. 3. Preferably, sixthlayer 74 has the same thickness and chemical composition as sixth layer42.

FIG. 7 illustrates preferred heat-shrinkable, multilayer film 76 for useas butt-seal tape film 60 in butt-seal backseamed casing 52 illustratedin FIG. 5. Multilayer film 76 comprises first layer 78, second layer 80,third layer 82, fourth layer 84, and fifth layer 86.

First layer 78 is an outer film layer which serves as a heat-seal layer,and is analogous to third layer 68 of film 62 illustrated in FIG. 6.First layer 78 serves as the outer layer of butt-seal tape film 60 whichis sealed to outside surface 55 of casing film 54, i.e., to form seals59 and 61 (see FIG. 5). Preferably, first layer 78 has the samethickness and chemical composition as third layer 68.

Second layer 80 is an inner film layer between first layer 78 and thirdlayer 82, serves as an O₂-barrier layer, and is analogous to fourthlayer 38 of multilayer film 30 illustrated in FIG. 3. Preferably, secondlayer 80 has the same thickness and chemical composition as fourth layer38.

Third layer 82 is an outer film layer which serves as a butt-seal tapeabuse-resistance layer, and is analogous in composition to third layer68 of film 62 illustrated in FIG. 6. Preferably, third layer 82 has thesame thickness and chemical composition as third layer 68.

Fourth layer 84 is an inner film layer which serves as a tie layer, isbetween first layer 78 and second layer 80, and is analogous to fifthlayer 40 of film 30 illustrated in FIG. 3. Preferably, fourth layer 84has the same thickness and chemical composition as fifth layer 40.

Fifth layer 86 is an inner film layer which serves as a tie layer, isbetween second layer 80 and third layer 82, and is analogous to sixthlayer 42 of film 30 illustrated in FIG. 3. Preferably, fifth layer 86has the same thickness and chemical composition as sixth layer 42.

It should be noted that the butt-seal tape film need not have a corelayer of polyamide or polyester which prevents the butt-seal tape filmfrom necking down on the forming shoe. This is due to the fact that thebutt-seal tape occupies so little of the overall structure of thebutt-sealed backseamed casing, that the shrinkage of the tape filmduring the backseaming operation has little tendency to cause neckingdown on the forming shoe.

Backseamed casings 11 and 52 (illustrated in FIGS. 1 and 5,respectively) which use films 12, 30, 44, 62, and 76 (illustrated inFIGS. 2, 3, 4, 6, and 7, respectively), are suited to many differentforms of packaging in accordance with the present invention, includingshirred casings, bags, etc.

FIG. 8 illustrates a preferred process for making casing film and/orbutt-seal tape film for in accordance with the present invention. Forexample, FIG. 8 illustrates a preferred process for making the filmsillustrated in FIGS. 2, 3, 4, 6, and 7. In the process illustrated inFIG. 8, solid polymer beads (not illustrated) are fed to a plurality ofextruders (for simplicity, only extruder 88 is illustrated). Insideextruders 88, the polymer beads are degassed, following which theresulting bubble-free melt is forwarded into die head 90, and extrudedthrough an annular die, resulting in tubing tape 92 which is preferablyfrom about 15 to 30 mils thick, and preferably has a lay-flat width offrom about 2 to 10 inches.

After cooling or quenching by water spray from cooling ring 94, tubingtape 92 is collapsed by pinch rolls 96, and is thereafter fed throughirradiation vault 98 surrounded by shielding 100, where tubing tubing 92is irradiated with high energy electrons (i.e., ionizing radiation) fromiron core transformer accelerator 102. Tubing tape 92 is guided throughirradiation vault 98 on rolls 104. Preferably, tubing tape 92 isirradiated to a level of from about 40-100 kGy, resulting in irradiatedtubing tape 106. Irradiated tubing tape 106 is wound upon windup roll108 upon emergence from irradiation vault 98, forming irradiated tubingtape coil 110.

After irradiation and windup, windup roll 108 and irradiated tubing tapecoil 110 are removed and installed as unwind roll 112 and unwind tubingtape coil 114, on a second stage in the process of making the film asultimately desired. Irradiated tubing 106, being unwound from unwindtubing tape coil 114, is then passed over guide roll 116, after whichirradiated tubing 106 is passed through hot water bath tank 118containing hot water 120. Irradiated tubing 106 is then immersed in hotwater 120 (preferably having a temperature of about 185-210° F.) for aperiod of about 20-60, i.e., for a time period long enough to bring thefilm up to the desired temperature for biaxial orientation. Thereafter,hot, irradiated tubular tape 122 is directed through nip rolls 124, andbubble 126 is blown, thereby transversely stretching hot, irradiatedtubular tape 122 so that an oriented film tube 128 is formed.Furthermore, while being blown, i.e., transversely stretched, nip rolls130 have a surface speed higher than the surface speed of nip rolls 124,thereby resulting in longitudinal orientation. As a result of thetransverse stretching and longitudinal drawing, oriented film tube 128is produced, this blown tubing preferably having been both stretched ina ratio of from about 1:1.5 to 1:6, and drawn in a ratio of from about1:1.5 to 1:6. More preferably, the stretching and drawing are eachperformed at a ratio of from about 1:2 to 1:4. The result is a biaxialorientation of from about 1:2.25 to 1:36, more preferably, 1:4 to 1:16.While bubble 126 is maintained between pinch rolls 124 and 130, orientedfilm tube 128 is collapsed by rollers 132, and thereafter conveyedthrough pinch rolls 130 and across guide roll 134, and then rolled ontowind-up roll 136. Idler roll 138 assures a good wind-up. The resultingmultilayer film can be used to form backseamed casings, etc., which, inturn, can be used for the packaging of meat products, in accordance witthe present invention.

The films of the examples set forth below were prepared according to theprocess described immediately above. These examples provide additionaldetails on the backseamed casings, their use in the packaging of a meatproduct, and the unexpected results obtained from the use of the casingfilm during the backseaming process, and subsequent packaging andcook-in of the meat product.

The polymer components used to fabricate multilayer casing film andbutt-seal tape film according to the present invention may also containappropriate amounts of additives typically included in suchcompositions. These additives include slip agents such as talc,antioxidants, fillers, dyes, pigments, radiation stabilizers, antistaticagents, elastomers, and like additives known to those of skill in theart of packaging films.

The backseamed casings according to the present invention comprisecasing films and butt-seal tape films which can be prepared by any meansknown to those of skill in the art, e.g., via coextrusion and/orextrusion coating, and/or lamination. However, preferably the films areproduced by coextrusion.

The backseamed casing according to the present invention preferablycomprises a casing film (and butt-seal tape film) which comprises acrosslinked polymer network. Although the crosslinked polymer networkcan be produced in one or more of a variety of manners, such as chemicalcrosslinking and/or irradiation, preferably the crosslinked polymernetwork is produced by the irradiation of a tape or film. Either some orall of the layers of the multilayer film can comprise crosslinkedpolymer networks.

In the irradiation process, the film is subjected to an energeticradiation treatment, such as high energy electron treatment, whichinduces cross-linking between molecules of the irradiated material. Theirradiation of polymeric films is disclosed in U.S. Pat. No. 4,064,296,to BORNSTEIN, et. al., which is hereby incorporated in its entirety, byreference thereto. BORNSTEIN, et. al. discloses the use of ionizingradiation for crosslinking the polymer present in the film.

Radiation dosages are referred to herein in terms of the radiation unit“RAD”, with one million RADS, also known as a megarad, being designatedas “MR”, or, in terms of the radiation unit kiloGray (kGy), with 10kiloGray representing 1 MR, as is known to those of skill in the art. Asuitable radiation dosage of high energy electrons is in the range of upto about 16-166 kGy, more preferably about 44-139 kGy, and still morepreferably, 50-80 kGy. Preferably, irradiation is carried out by anelectron accelerator and the dosage level is determined by standarddosimetry methods.

As used herein, the phrases “corona treatment” and “corona dischargetreatment” refer to subjecting the surfaces of thermoplastic materials,such as polyolefins, to corona discharge, i.e., the ionization of a gassuch as air in close proximity to a film surface. The ionization isinitiated by a high voltage passed through a nearby electrode, causingoxidation and other changes to the film surface.

Corona treatment of polymeric materials is disclosed in U.S. Pat. No.4,120,716, to BONET, issued Oct. 17, 1978, which is hereby incorporatedin its entirety by reference thereto. BONET discloses improved adherencecharacteristics of polyethylene, by subjecting of the polyethylene tocorona treatment, in order to oxidize the surface thereof. U.S. Pat. No.4,879,430, to HOFFMAN, also hereby incorporated in its entirety byreference thereto, discloses the use of corona discharge for thetreatment of plastic webs for use in meat cook-in packaging, with thecorona treatment of the inside surface of the web increasing theadhesion of the film to the proteinaceous material.

Although corona treatment is a method of treatment of the multilayerfilm of the present invention, plasma treatment of the film may also beused.

FIG. 9 illustrates a perspective view of package 140 in accordance withthe present invention, and FIG. 10 illustrates a cross-sectional viewthrough section 10—10 of FIG. 9. Package 140 comprises lap-seal casing144 which encases meat product 146, with casing 144 being closed at bothends by clips 142, with only one clip being illustrated in FIG. 9. Thelap seal portion of casing 144 comprises longitudinal outer casing filmedge 148 and longitudinal inner casing film edge 150, as well as overlapregion 152 which contains the backseam seal. Casing 144 comprises amultilayer casing film in accordance with the backseamed casing of thepresent invention. The casing film can be, for example, any one or moreof preferred multilayer films 12, 30, 44, or 62, as described in detailabove. Furthermore, although package 140 as illustrated comprises alap-seal casing, alternatively the package can comprise a butt-sealcasing (preferably, as illustrated in FIG. 5), in which latter instancethe casing further comprises a butt-seal tape, preferably as describedabove and as illustrated in FIGS. 5 and 7. In FIGS. 9 and 10, product146 in the package is preferably meat, more preferably cooked meat, andpreferably inside surface 154 of casing 144 is adhered to the meatproduct during cook-in.

The packaged product can be made by a process comprising: (A) filling abackseamed casing with a meat product, whereby a filled casing isformed; (B) closing the ends of the filled casing so that the meatproduct is encased by the backseamed casing, whereby a chub is formed;and (C) cooking the meat product encased in the backseamed casing bysubjecting the chub to cook-in, so that the meat product adheres to theinside surface of the casing. The backseamed casing is a backseamedcasing according to the present invention, preferably a preferredbackseamed casing according to the present invention.

Although in general the product in the package can be any cooked meatproduct, preferably the cooked meat product comprises at least onemember selected from the group consisting of poultry, ham, beef, lamb,goat, horse, fish, liver sausage, mortadella, and bologna; morepreferably, poultry, ham, beef and bologna; even more preferably, hamand roast beef.

The invention is illustrated by the following examples, which areprovided for the purpose of representation, and are not to be construedas limiting the scope of the invention. Unless stated otherwise, allpercentages, parts, etc. are by weight.

EXAMPLE 1

A 3¾ inch wide (lay flat dimension) tube, called a “tape”, was producedby the coextrusion process described above and illustrated in FIG. 8,wherein the tape cross-section (from inside of tube to outside of tube)was as follows:

3.0 mils of LLDPE#1 (80%) and Ionomer #1 (20%)/

3.2 mils of a blend of EVA#1 (80%) and LMDPE#1 (20%)/

1.8 mil of anhydride grafted LLDPE#2/

1.6 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)/

0.8 mil of EVOH/

0.8 mils of anhydride grafted LLDPE#2/

2.7 mils of a blend of EVA#1 (80%) and LMDPE#1 (20%)/

3.5 mils of LLDPE #3;

wherein:

LLDPE#1 was DOWLEX® 2045.03 linear low density polyethylene, obtainedfrom Dow Plastics, of Freeport, Tex.;

Ionomer#1 was SURLYN® 1650 zinc-based ionomer of ethylene/methacrylicacid copolymer, obtained from E. I. DuPont de Nemours, of Wilmington,Del.;

LLDPE#2 was TYMOR® 1203 linear low density polyethylene having ananhydride functionality grafted thereon, obtained from MortonInternational, of Chicago, Ill.;

EVA#1 was PE 5269T (TM) ethylene vinyl acetate copolymer, obtained fromChevron Chemical Company of Houston, Tex.;

EVOH was EVAL® LC-E105A polymerized ethylene vinyl alcohol, obtainedfrom Eval Company of America, of Lisle, Ill.;

LMDPE#1 was DOWLEX® 2037 linear medium density polyethylene, obtainedfrom Dow Plastics, of Freeport, Tex.;

NYLON#1 was ULTRAMID® B4 polyamide 6, obtained from BASF corporation ofParsippany, N.J.;

NYLON#2 was GRILON® CF6S polyamide 6/12, obtained from EMS-AmericanGrilon Inc., of Sumter, S.C.;

LLDPE#3 was DOWLEX® 2244A linear low density polyethylene, obtained fromDow Plastics of Freeport, Tex.;

All the resins were extruded between 380° F. and 500° F., and the diewas heated to approximately 420° F. The extruded tape was cooled withwater and flattened, the flattened width being 3¾ inches wide in alay-flat configuration. The tape was then passed through a scanned beamof an electronic cross-linking unit, where it received a total dosage of64 kilo Grays (kGy), which is the equivalent of 4.5 mega Rads (MR).After irradiation, the flattened tape was passed through hot water forabout a third of a minute, the hot water having a temperature of fromabout 208° F. to 210° F. The resulting heated tape was inflated into abubble and oriented into a film tubing having a lay-flat width of 9¾inches and a total thickness of 2.3 mils. The bubble was very stable andthe optics and appearance of the film were good. The film tubing wasdetermined to have 18% free shrinkage in the longitudinal direction and29% free shrinkage in the transverse direction, when immersed in hotwater for about 8 seconds, the hot water being at a temperature of 185°F., i.e., using ASTM method D2732-83.

The film tubing, made as described immediately above, was then slit sothat it was converted into film sheet. The film sheet was foldedlongitudinally around a forming shoe with opposing lengthwise film sheetedges being overlapped. Thereafter, a lap-seal backseam casing was madeby applying a heat seal (using a hot seal bar, more particularly aNishibe Model HSP-250-SA sealing machine) longitudinally over theoverlapping regions of the film sheet. During the backseaming operation,the film was positioned so that the outside layer of the film tubing(before it was slit) formed the outside layer of the backseamed casing,with the inside layer of the film tubing forming the inside layer of thebackseamed casing. The film backseamed well, i.e., without necking downaround the forming shoe to the extent that the film ruptured or theprocess was interrupted.

The resulting backseamed casing, having with a lay-flat width of about 4inches, was then clipped at one end and filled with chopped ham emulsionfrom the open end. The casing was then closed with a second metal clipand the section of meat-filled casing was cut free of the remainder ofthe casing, forming a package which comprises the lap-seal backseamedcasing and the ham emulsion encased in the casing. Several such packageswere produced, and were thereafter cooked for about 4 hours at fromabout 145° F.-170° F. in a high humidity environment. The cooked casingswere then cooled in a cooler kept at 32° F. for several hours. Theresulting chilled packages were then examined for purge and found tohave no purge between the cooked meat product and the casing film. Also,several samples of backseamed casing were made, each containing water asthe packaged medium, and a mixture of 0.1% mineral oil and 99.9% water.These casings were evaluated for seal strength survivability by cookingat 180° F. for 12 hrs, and were found to have acceptable seal strength.

The backseamed casing was also shirred. The shirred casings were foundto have acceptable seal strength, with very few or no pinholes beingdetected.

EXAMPLE 2

A 3¾ inch wide (lay flat dimension) tape is produced by the coextrusionprocess described above in FIG. 8, wherein the tape cross-section (frominside to outside) is as follows:

6.0 mils of LLDPE#3 (80%) and ION#1 (20%)/

1.1 mil of anhydride grafted LLDPE#2/

2.0 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)/

1.1 mil of EVOH/

1.1 mils of anhydride grafted LLDPE#2/

6.0 mils of LLDPE #3,

wherein all the resins are as identified in Example 1 above. All theresins are extruded at a temperature of from about 380° F. to 500° F.,and the die is at approximately 420° F. The extruded tape is cooled withwater and flattened, the flattened width being 3¾ inches wide, in alay-flat configuration. The tape is then passed through a scanned beamof an electronic cross-linking unit, where it receives a total dosage of64 kilo Grays (kGy), which is the equivalent of 4.5 mega Rads (MR).After irradiation, the flattened tape is passed through hot water at208° F. to 210° F. for a period of about a third of a minute,immediately after which the heated tape is inflated into a bubble, andis oriented into tubing having a lay-flat width of 9¾ inches and a totalthickness of 2.3 mils. The bubble is stable and the optics andappearance of the film are good. The resulting film has 18% freeshrinkage in the longitudinal direction and 29% free shrinkage in thetransverse direction when it is immersed in hot water at 185° F., i.e.,using ASTM method D2732-83.

The film tubing, made as described immediately above, is then slitlengthwise, converting the film tubing into film sheet. The film sheetis folded longitudinally around a forming shoe with longitudinallyopposing edges being overlapped, with the overlapping regions thereafterbeing joined by applying a heat seal, using a hot-seal bar,longitudinally over the overlap, to form a lap seal using a NishibeModel HSP-250-SA sealing machine. During the backseaming operation, thefilm is positioned so that the outside layer of the film tubing (beforeit is slit) corresponds with the outside layer of the backseamed casing,with the inside layer of the film tubing corresponding with the insidelayer of the backseamed casing. The film backseams well.

The resulting backseamed casing, having a lay-flat width of about 4inches, is then clipped at one end and filled with chopped ham emulsionfrom the open end. The tubing is then closed with a second metal clipand the section of meat-filled casing is cut free of the remainder ofthe casing, forming a package which comprises the lap-seal backseamedcasing and the ham emulsion encased in the casing. Several packages areso made. Each of the packages is cooked for about 4 hours from 145°F.-170° F. in a high humidity environment. The cooked packages are thencooled in a cooler kept at 32° F. for several hours. The resultingcooked, chilled packages are examined for purge and found to have nopurge between the cooked meat product and the inside surface of thebackseamed casing.

Several additional packages are made from the backseamed casing, each ofthese packages containing a product comprising 99.9% water and 0.1%mineral oil. These casings are evaluated for seal strength survivabilityby cooking at 180° F. for 12 hours, and are found to have acceptableseal strength.

EXAMPLE 3

A 3¾ inch wide (lay flat dimension) tubular tape is produced accordingto Example 1. The tape cross-section (from inside of tube to outside oftube) is as follows:

6.0 mils of Terpolyolefin#1/

1.1 mil of anhydride grafted LLDPE#2/

2.0 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)/

1.1 mils of EVOH/

1.1 mils of anhydride grafted LLDPE#2/

6.0 mils of LLDPE #3,

wherein:

Terpolyolefin#1 is LOTADER® 3210 ethylene/butyl acrylate/maleicanhydride terpolymer, comprising about 3% anhydride functionality,obtained from Elf Atochem North America, Inc., of Philadelphia, Pa., andall the other resins areas identified in Example 1 above.

All the resins are extruded between 380° F. and 500° F., and the die isat approximately 420° F. The extruded tape is cooled with water andflattened, the flattened width being 3¾ inches wide, in a lay-flatconfiguration. The tape is then passed through a scanned beam of anelectronic cross-linking unit, where it receives a total dosage of 64kilo Grays (kGy), which is the equivalent of 4.5 mega Rads (MR). Afterirradiation, the flattened tape is passed through hot water at 208° F.to 210° F., inflated into a bubble, and oriented into tubing having alay-flat width of 9¾ inches and a total thickness of 2.3 mils. Thebubble is stable and the optics and appearance of the resulting tubingfilm are good. The tubing film has 18% free shrinkage in thelongitudinal direction and 29% free shrinkage in the transversedirection, when immersed in hot water for 8 seconds at 185° F., i.e.,according to ASTM method D2732-83.

The tubing film is then slit into film. The film is foldedlongitudinally around a forming shoe with opposing longitudinal edgesbeing overlapped, with the overlapping regions then being joined byapplying a heat seal (using a hot-seal bar) longitudinally over theoverlap, to form a lap-seal backseamed casing, using a Nishibe ModelHSP-250-SA sealing machine. During the backseaming operation, the filmis positioned so that the layer which corresponds with the outside layerof the film tubing (before it is slit) forms the outside layer of theresulting backseamed casing, with the layer which corresponds with theinside layer of the film tubing forms the inside layer of the resultinglap-seal backseamed casing. The film backseams well, i.e., withoutnecking down on the forming shoe to the extent that the film eitherruptures or interrupts the process.

This resulting backseamed casing, having a lay-flat width of about 4inches, is then clipped at one end and filled from the open end withchopped ham emulsion. The tubing is then closed with a second metalclip, resulting in a package, with the package thereafter being cookedfor about 4 hours from 145° F.-170° F. in a high humidity environment.The packages containing cooked ham emulsion are then cooled in a coolerfor several hours, the cooler having a temperature of about 32° F. Theresulting chilled packages are then examined for purge and found to haveno purge between the product and the plastic material.

Several other backseamed casings are filled with a mixture of 99.9%water and 0.1% mineral oil. These casings are evaluated for sealstrength survivability by cooking at 180° F. for 12 hrs, and are foundto have acceptable seal strength.

EXAMPLE 4

A 3¾ inch wide (lay flat dimension) annular tape, was produced by thecoextrusion process described above and illustrated in FIG. 5, whereinthe tape cross-section (from inside to outside) was as follows:

2.8 mils of EMAA#1/

3.3 mils of a blend of EVA#1 (80%) and HDPE#1 (20%)/

0.9 mils of anhydride grafted LLDPE#2/

1.8 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)/

1.1 mils of EVOH/

1.6 mils of anhydride grafted LLDPE#2/

2.2 mils of a blend of EVA#1 (80%) and HDPE#1 (20%)/

3.1 mils of LLDPE #3,

wherein:

EMAA#1 was NUCREL® ARX 84-2 ethylene/methacrylic acid copolymer,obtained from E. I. DuPont de Nemours, of Wilmington, Del.;

HDPE#1 is FORTIFLEX® J60-500C-147 high density polyethylene, obtainedfrom Solvay Polymers, Inc., Deer Park, Tex.; and

all other resins are as identified in Example 1 above.

All the resins were extruded at a temperature of from about 380° F. to500° F., and the die was heated to approximately 420° F. The extrudedtape was cooled with water and flattened, the flattened width being 3¾inches wide, in a lay-flat configuration. The tape was then passedthrough a scanned beam of an electronic cross-linking unit, where itreceived a total dosage of 64 kilo Grays (kGy), which is the equivalentof 4.5 mega Rads (MR). After irradiation, the flattened tape was passedthrough hot water at 208° F. to 210° F., inflated into a bubble, andoriented into film tubing having a lay-flat width of 9¾ inches and atotal thickness of 2.3 mils. The bubble was very stable and the opticsand appearance of the film tubing were good. The resulting film tubinghad 18% free shrinkage in the longitudinal direction and 29% freeshrinkage in the transverse direction, when immersed for 8 seconds inhot water at 185° F., i.e., using ASTM method D2732-83.

The film tubing, made as described immediately above, was then slitlongitudinally, thereby converting the film tubing into film sheet. Thefilm sheet was folded longitudinally around a forming shoe, withopposing longitudinal edges being overlapped, with the overlappingregions of the film sheet thereafter being joined by applying a heatseal (using a hot-seal bar) longitudinally over the overlap, using aNishibe Model HSP-250-SA sealing machine. During the backseamingoperation, the film was positioned so that the outside layer of the filmtubing (before it was slit) corresponds to the outside layer of theresulting backseamed casing, with the inside layer of the film tubingcorresponding to the inside layer of the backseamed casing. The filmbackseamed well and appeared to have acceptable seal strength. The filmwas also evaluated for protein adhesion and found to have satisfactorypurge resistance with an intermediate quality ham product.

EXAMPLE 5

A 5¾ inch wide (lay flat dimension) annular tape was produced by thecoextrusion process described above and illustrated in FIG. 8, whereinthe tape cross-section (from inside the tube to outside the tube) was asfollows:

3.0 mils of LLDPE#3 (80%) and EAA#1 (20%)/

3.4 mils of a blend of EVA#1 (60%), HDPE#1 (20%) and PIG#1 (20%)/

1.2 mil of anhydride grafted LLDPE#2/

1.7 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)/

1.0 mils of EVOH/

1.1 mils of anhydride grafted LLDPE#2/

2.7 mils of a blend of EVA#1 (60%), EAA#1 (20%) and PIG#1 (20%)/

3.4 mils of LLDPE #3,

wherein:

EAA#1 is PRIMACOR® 1410 ethylene/acrylic acid copolymer, obtained fromThe Dow Chemical Company, of Midland, Mich.;

PIG#1 is EPE 10214-C opaque white color concentrate, obtained fromTeknor Color Company, of Pawtucket, R.I.;

all other resins were as identified in Examples 1-4, above.

All the resins were extruded at a temperature of from about 380° F. to500° F., and the die was heated to approximately 420° F. The extrudedtape was cooled with water and flattened, the flattened width being 5¾inches, in a lay-flat configuration. The tape was then passed through ascanned beam of an electronic cross-linking unit, where it received atotal dosage of 64 kilo Grays (kGy), which is the equivalent of 4.5 megaRads (MR). After irradiation, the flattened tape was passed through hotwater for about a third of a minute, the hot water having a temperatureof from about 208° F. to 210° F. Immediately upon emerging from the hotwater bath, the heated tape was inflated into a bubble, and orientedinto a film tubing having a lay-flat width of 15 inches and a totalthickness of 2.3 mils. The bubble was very stable and the optics andappearance of the film tubing were good. The resulting film tubing had18% free shrinkage in the longitudinal direction and 29% free shrinkagein the transverse direction when immersed in hot water at 185° F. for 8seconds, i.e., using ASTM method D2732-83.

The tubing, made as described immediately above, was then slit intofilm, and was converted into a lap-seal backseamed casing in the mannerdescribed in Example 1, above. The film backseamed very well.

The lap-seal backseamed casing, having a lay-flat width of about 4inches, was then clipped at one end and filled with chopped ham emulsionfrom the open end. The casing was then closed with a second metal clip,and the section of meat-filled casing is cut free of the remainder ofthe casing, forming a package which comprises the lap-seal backseamedcasing and the ham emulsion encased in the casing. Several packages wereproduced in this manner, with the packages thereafter being cooked forabout 4 hours at a temperature of from 145° F. to 170° F., in a highhumidity environment. The resulting cooked casings were then cooled in acooler kept at 32° F. for several hours. The resulting chilled casingswere then examined for purge and found to have no purge between theproduct and the plastic material.

Several additional packages were produced, these additional packagesusing the same backseamed casing, but encasing a product containing99.9% water and 0.1% mineral oil. These casings were evaluated for sealstrength survivability by cooking at 180° F. for 12 hrs, and were foundto have acceptable seal strength.

The slit film was also corona-treated to a surface energy level of 62dynes/cm, and then immediately folded (and overlapped) longitudinallyabout a second forming shoe having a size so that the resulting lap-sealbackseamed casing had a lay-flat width of about 5¼ inches. Thisbackseamed casing was then clipped at one end and filled with liversausage emulsion from the open end. The casing was then closed with asecond metal clip, and the section of meat-filled casing was cut free ofthe remainder of the casing, forming a package which comprised thelap-seal backseamed casing and the liver sausage emulsion encased in thecasing. Several packages were produced in this manner, with the packagesthereafter being cooked for about 4 hours from 145° F.-170° F. in a highhumidity environment. The resulting packages containing cooked meat werethen cooled in a cooler kept at 32° F. for several hours. The resultingchilled packages were then examined for purge and found to have goodpurge-resistance at the casing lay-flat edges, i.e., where the edges hadrubbed against the forming shoe. Thus, even though the corona treatmentat the casing lay-flat edges had been ‘buffed off’, there was stillsufficient affinity of the untreated meat-contact surface of the casing(comprising ethylene/acrylic acid copolymer) to the liver sausage toprevent fatting out at that location.

The above backseamed casing was also shirred. The shirred casings werefound to have acceptable seal strength, with very few or no pinholesbeing detected.

EXAMPLE 6

A 5-inch tape was produced by the coextrusion process described aboveand illustrated in FIG. 8, wherein the tape cross-section (from insideof tube to outside of tube) was as follows:

3.0 mils of LLDPE #4/

5.0 mils of a blend of EVA#2 (80%) and LLDPE #1 (20%)/

1.0 mil of anhydride grafted LLDPE#2/

2.5 mils of Nylon#2/

1.1 mils of EVOH/

1.6 mils of anhydride grafted LLDPE#2/

2.4 mils of a blend of EVA#2 (80%) and LLDPE#1 (20%)/

3.0 mils of LLDPE #3, and

wherein:

LLDPE#4 was PLEXAR® PX 360 anhydride grafted linear low densitypolyethylene, obtained from Quantum Chemical Company, of Cincinnati,Ohio;

EVA#2 was ELVAX® 3128 ethylene/vinyl acetate copolymer, obtained from E.I. DuPont de Nemours & Co., of Wilmington, Del.; and

and all other the resins are as identified in Examples 1-5, above.

The tape was made and oriented into 15-inch wide tubing film in themanner described in Example 1, above. One significant difference betweenthis film and the films of Examples 1-5 is that the film of this examplehas a core layer comprising only Nylon #2, i.e., nylon 6/12, rather thancontaining the blend of nylon 6 and nylon 6/12. The tape orientedacceptably, though its orientability was/is significantly inferior tothat of the tapes of Examples 1-5.

The film tubing was converted into film sheet, which in turn wasconverted into lap-seal backseamed casing in the manner described inExample 1, above. The film backseamed acceptably, though not as well asthe films of Examples 1-5. Also, when evaluated for seal strength, itwas/is discovered that, while the backseamed tubing of this exampleprobably had acceptable seal strength, its seal strength was/is inferiorto that of the films of Examples 1-5.

EXAMPLE 7 (COMPARATIVE)

A 5⅛ inch, lay-flat width, annular tape was produced by the coextrusionprocess described above and illustrated in FIG. 8, wherein the tapecross-section (from inside the tube to outside the tube) was as follows:

3.2 mils of LLDPE #4/

5.2 mils of a blend of EVA#2 (65%), LLDPE #1 (20%) and PIG#1 (15%)/

0.9 mils of anhydride grafted LLDPE#2/

0.7 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)/

1.1 mil of EVOH/

1.7 mils of anhydride grafted LLDPE#2/

1.9 mils of a blend of EVA#2 (65%), LLDPE#1 (20%) and PIG#1 (15%)/

3.2 mils of LLDPE#3,

wherein all the resins are as identified in Examples 1-6 above.

All the resins were extruded at a temperature of from about 380° F. and530° F., and the die was heated to approximately 420° F. The extrudedtape was cooled with water and flattened, and had a width of about 5⅛inches. This tape was then passed through the scanned beam of anelectronic crosslinking unit where the tape received a total dosage of64 kGy. After irradiation, the flattened tape was passed through hotwater for about a third of a minute, the hot water having a temperatureof from about 204° F. to 210° F. The resulting heated tape was theninflated into a bubble in a manner so that the heated tape was convertedinto a biaxially oriented film tubing. The oriented film tubing had alay-flat width of 15 inches. The multilayer film having a totalthickness of 2.3 mils, and a free shrink in the longitudinal directionof about 18 percent, and 29 percent in the transverse direction. Freeshrink was determined by immersing the film in hot water at 185° F. forabout 8 seconds, i.e., using ASTM method D2732-83.

The tubing, made as described immediately above, was then slit intofilm. The film was folded longitudinally about a forming shoe withopposed edges being joined by applying a heat seal longitudinally overthe overlapping regions of the film, in an attempt to form a lap sealusing a Nishibe Model HSP-250-SA sealing machine. During the backseamingoperation, the film was positioned so that the outside layer of thetubing (before it was slit) corresponded with the outside layer of thebackseamed tubing, with the inside layer of the tubing correspondingwith the inside layer of the backseamed tubing. However, during thisbackseaming step, the film necked down a substantial degree on theforming shoe, resulting in intermittent film rupture. Thus, the film wasnot backseamable.

EXAMPLE 8

A 3½ inch lay-flat annular tape was produced by the coextrusion processdescribed above and illustrated in FIG. 8, wherein the tapecross-section (from inside of tube to outside of tube) was as follows:

3.2 mils of LLDPE #4/

4.9 mils of a blend of EVA#2 (65%), LLDPE #1 (20%) and PIG#1 (15%)/

1.0 mil of anhydride grafted LLDPE#2/

2.5 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)/

1.2 mil of EVOH/

1.6 mils of anhydride grafted LLDPE#2/

1.9 mils of a blend of EVA#2 (65%), LLDPE#1 (20%), and PIG#1 (15%)/

3.2 mils of LLDPE #3,

wherein all resins are as identified in Example 7 (Comparative), as setforth above.

The tape was made and oriented into 10 inch tubing film in a manner asdescribed above in Example 7 (Comparative). The only substantialdifference between the film of this example and the film of Example 7(Comparative) is the thickness of the nylon core layer, i.e., in thisexample, the nylon core layer was about 3½ times as thick as thethickness of the nylon core layer in the film of Example 7(Comparative).

The resulting film tubing was converted into film sheet and wasthereafter further converted into a backseamed casing, these conversionprocesses being carried out in the same manner as set forth in Example 7(Comparative), above. However, contrary to the film of Example 7(Comparative), this film did not undergo substantial necking down on theforming shoe, and underwent backseaming successfully.

Although the casing of this example did not have sufficient purgeresistance, this example demonstrated that a minimum thickness of thenylon core layer is critical to the backseamability of a heat-shrinkablefilm.

The backseamed casing was also shirred. The shirred casings were foundto have acceptable seal strength, with very few or no pinholes beingdetected.

EXAMPLE 9 (COMPARATIVE)

A 5⅛ inch tubular tape was produced by the coextrusion process describedabove and illustrated in FIG. 8, wherein the tape cross-section (frominside of tube to outside of tube) was as follows:

3.0 mils of a blend of LLDPE #4 (90%) and NYLON#2 (10%)/

5.2 mils of a blend of LLDPE #2 (80%) and EAO#1 (25%)/

2.0 mil of anhydride grafted LLDPE#2/

1.1 mil of EVOH/

1.7 mils of anhydride grafted LLDPE#2/

3.2 mils of a blend of LLDPE#2 (80%) and EAO#1 (20%)/

3.0 mils of LLDPE#3,

wherein EAO#1 was EXACT 4011 (TM) homogeneous ethylene/alpha-olefincopolymer, obtained from the Exxon Chemical Company, of Baytown, Tex.;and all other resins are as identified in Examples 1-5 and Comparatives1-2 above.

All the resins were extruded at a temperature of from about 380° F. to530° F., and the die was at a temperature of about 420° F. The extrudedtape was cooled with water and flattened, the flattened width being 5⅛inches. This tape was then passed through the scanned beam of anelectronic crosslinking unit where it received a total dosage of 64 kGy.After irradiation, the flattened tape was passed through hot water forabout a third of a minute, the hot water having a temperature of fromabout 204° F. to 210° F. Upon emerging from the hot water, the resultingheated tape was immediately inflated into a bubble, and oriented toresult in an oriented film tube having a lay-flat width of 14 inches.This film had a total thickness of 2.3 mils. The tape did not orient aswell as the films described in Example 1, 4, 5, 7 (comparative), and 8(comparative), due to the absence of the nylon core layer. The film hada free shrink of about 25 percent in the longitudinal direction, andabout 29 percent in the transverse direction. Free shrink was determinedby immersing the film in hot water for about 8 seconds, the water havinga temperature of about 185° F., i.e., using ASTM method D2732-83.

The tubing film was converted into film sheet which was backseamed asdescribed in Example 1. However, during backseaming the film necked downseverely on the forming shoe (much more severely than in the case ofExample 7 (Comparative), thereby rupturing itself and disrupting theprocess. Thus, this film was not a viable backseamable film. Thus, notonly did the absence of the nylon core layer affect orientability of thefilm, but the resulting film also was not backseamable. This comparativeexample highlights the importance of the nylon core layer, forbackseaming as well as orientability.

EXAMPLE 10

A 5⅛ inch tubular tape was produced by the coextrusion process asdescribed above and illustrated in FIG. 8, wherein the tapecross-section (from inside the tube to outside the tube) was as follows:

3.0 mils of a blend of LLDPE#4 (80%) and NYLON#2 (20%)/

6.0 mils of a blend of LLDPE#2 (80%) and EAO#1 (20%)/

1.0 mil of anhydride grafted LLDPE#2/

1.6 mils of a blend of NYLON#1 (50%) and NYLON#2 (50%)/

1.0 mil of EVOH/

1.7 mils of anhydride grafted LLDPE#2/

3.0 mils of a blend of LLDPE#2 (80%) and EAO#1 (20%)/

3.0 mils of LLDPE#3,

wherein all resins are as identified in Examples 1-9 above. The tape wascoextruded and oriented into 14 inch wide tubing film as described abovein Example 9 (Comparative). The only substantial difference between thisfilm and the film of Example 9 (Comparative) was the incorporation ofthe nylon core layer in the film of this example. The film orientedacceptably and far superior to the film of Example 9 (Comparative). Thetubing was then slit into film and was backseamed by a process asdescribed in Example 1 above. The film backseamed well, and exhibitedgood seal strength.

However, even though the film of this example backseamed acceptably, itis not a preferred film because it exhibited insufficient proteinadhesion, i.e., insufficient purge-resistance. However, a comparison ofthe backseamability of this film with the backseamability andorientability of the film of Example 9 (Comparative), indicate that thepresence of the nylon core layer is critical to both backseamability andorientability of the resulting heat-shrinkable film.

EXAMPLE 11

A 5-inch tubular tape was produced by the coextrusion process describedabove and illustrated in FIG. 8, wherein the tape cross-section (frominside the tube to outside the tube) was as follows:

3.2 mils of LLDPE #4/

4.6 mils of a blend of EVA#2 (80%) and LLDPE #1(20%)/

1.0 mil of anhydride grafted LLDPE#2/

1.9 mils of a blend of Nylon#1 (50%) and Nylon#2 (50%)/

1.1 mil of EVOH/

1.9 mils of anhydride grafted LLDPE#2/

3.2 mils of a blend of EVA#2 (80%) and LLDPE#1 (20%)/

3.1 mils of LLDPE #3, and

wherein all the resins are as identified in Example 7 (Comparative),above. The tape was made and oriented into 15 inch lay-flat width filmtubing in the manner described above in Example 8. The only substantialdifference between this film of this example and the film of Example 8is that the film of this example was pigmented. The film was convertedinto film sheet and was backseamed as described in Example 1, above. Thefilm sheet backseamed well.

The backseamed casing was then used to prepare a number of packageswhich contained intermediate quality ham emulsion. The ham emulsion wasprepared, cooked, and chilled in the manner described in Example 1. Theresulting chilled packages were found to have significant andunacceptable purge between the meat-contact surface and the cooked meatproduct. Thus, this example indicates that the protein-adhesioncharacteristic of Plexar® PX 360 anhydride-containing polyolefin resin,which comprises less than about ½% anhydride functionality, isinsufficient for purge resistance with intermediate or poor quality hamproducts, i.e., products which are relatively low in protein, and aretherefore more difficult for obtaining film-to-meat adhesion. The hamproduct was the same as the ham product used in Example 1.

The film sheet was also corona-treated to a surface energy level of 62dynes/cm, and thereafter backseamed, with the resulting backseamedcasing being used as described immediately above, i.e., to packageintermediate quality ham product. In an examination of the chilledcasings, purge was found at areas of the casing corresponding to thelay-flat edges, i.e., where the edges had rubbed against the formingshoe, thereby causing insufficient protein adhesion. The rubbing of theedges on the forming shoe presumably “buffed” the corona treated surfaceat that location. The buffing off of the corona treatment by the formingshoe resulted in too little purge resistance. Without corona treatment,the purge-resistance afforded by the anhydride-containing meat-contactresin (Plexar® PX360, which comprises less than 1% anhydridefunctionality), without corona treatment (since it had been buffed off),is insufficient to prevent fatting out. The liver sausage product usedis the same product used in the liver sausage cook-testing of Example 5.

The backseamed casing was also shirred. The shirred casings were foundto have acceptable seal strength, with very few or no pinholes beingdetected.

EXAMPLE 12 (COMPARATIVE)

A 4-inch tape was produced by the coextrusion process described above inFIG. 8 wherein the tape cross-section (from inside of tube to outside oftube) was as follows:

3.0 mils of EPC#1/

5.0 mils of a blend of EVA#3 (70%) and EAO#2 (30%)/

1.4 mil of anhydride grafted LLDPE#2/

1.2 mils of EVOH/

1.3 mils of anhydride grafted LLDPE#2/

5.0 mils of EPC#1,

and wherein:

EPC#1 was ELTEX P KS409, a propylene/ethylene copolymer, obtained fromfrom Solvay Polymers, Inc., of Deer Park, Tex.

EVA#3 was PE1651CS28, 6.5% EVA copolymer, obtained from RexeneCorporation, of Dallas, Tex.

EAO#2 was TAFMER (TM) P-0480, an ethylene/propylene copolymer, obtainedfrom Mitsui Petrochemical Industries, Ltd., of Tokyo, Japan; and

all the other resins are as identified in Example 1 above.

The tape was made and oriented into 12 inch wide tubing film in a manneras described in Example 1, above. The tape oriented acceptably, thoughthe orientability of the tape was inferior to the orientability of thetape of Example 1, probably because the tape of Example 1 contained acore layer comprising nylon.

The casing film, made as described immediately above, was then slit intofilm sheet. The film sheet was then corona treated on a flat-sheetcorona treater to achieve a surface energy level of about 48 dynes/cm onthe inside layer of the tubing film, i.e., the outer film layer whichwas to form the corona-treated inside layer of the casing. After coronatreating, the film sheet was folded longitudinally about a forming shoewith opposing edges being overlapped as described above. The resultingoverlapping region of the film was then joined by applying a heat seallongitudinally to the overlap, to form a lap seal, using a Nishibe ModelHSP-250-SA sealing machine. During the backseaming operation, the filmwas positioned so that the corona-treated surface formed the insidelayer of the resulting lap-seal casing. Although the film did notcontain a core layer comprising nylon and/or polyester, the filmbackseamed acceptably. It is believed that the presence of the outerfilm layers comprising propylene/ethylene copolymer assisted inpreventing the film from shrinking back so tightly against the formingshoe that the process would have been interrupted.

The backseamed casing was then used to prepare a number of packageswhich contained liver sausage. The packages were prepared, cooked, andchilled in the manner described in Example 1. While the lap-sealbackseamed casing was found to have reasonable seal strength, it was notas preferred as the casing of the present invention, due to less sealstrength during cook-in, and more seal pucker after cook-in, comparedwith the casing films of Examples 1 and 5. Furthermore, it was foundthat during cook-in fatting out occurred at regions corresponding withthe casing lay-flat edges, i.e., where the corona-treatment had beenbuffed off by the forming shoe.

EXAMPLE 13

A 5-inch tape was produced by the coextrusion process described aboveand illustrated in FIG. 8, wherein the tape cross-section (from insideof tube to outside of tube) was as follows:

3.7 mils of a blend of EPC#2 and EAO#3/

2.7 mils of anhydride grafted LLDPE#2/

2.0 mils of Nylon#2/

1.0 mils of EVOH/

2.6 mils of anhydride grafted LLDPE#2/

4.0 mils of a blend of EPC#2 and EAO#3,

and wherein:

EPC#2 was NOBLEN (TM) W531D propylene/ethylene copolymer, obtained fromSumitomo Chemical Company, Limited, of Tokyo, Japan;

EAO#3 was TAFMER (TM) A-4085, an ethylene-butene copolymer obtained fromMitsui Petrochemical Industries, Ltd., of Tokyo, Japan; and

all the other resins are as identified in Example 1 above.

The tape was made and oriented into 14-inch wide tubing film in a manneras described in Example 1, above. The tape oriented acceptably, thoughthe orientability of the tape was inferior to the orientability of thetape of Example 1, probably because the tape of Example 1 contained acore layer comprising a more preferred nylon composition.

The casing film, made as described immediately above, was then slit intofilm sheet and corona treated and backseamed in the manner described inExample 12, above. The film backseamed acceptably. After making chubsfrom the casing film packed with liver sausage and subjecting the chubsto cook-in as described in Example 12, the lap-seal backseamed casingwas found to have reasonable seal strength, it was not as preferred asthe casing of the present invention, due to less seal strength duringcook-in, and more seal pucker after cook-in, compared with the casingfilms of Examples 1 and 5. Furthermore, it was found that during cook-infatting out occurred at regions corresponding with the casing lay-flatedges, i.e., where the corona-treatment had been buffed off by theforming shoe.

EXAMPLE 14

A 5½-inch tape was produced by the coextrusion process described abovein FIG. 8 wherein the tape cross-section (from inside of tube to outsideof tube) was as follows:

2.8 mils of EPC#1/

5.9 mils of a blend of EVA#3 (70%) and EAO#2 (30%)/

1.5 mil of anhydride grafted LLDPE#2/

1.2 mils of EVOH/

3.0 mils of NYLON#2/

0.9 mils of anhydride grafted LLDPE#2/

2.4 mils of a blend of EVA#3 (70%) and EAO#2 (30%)/

2.9 mils of EPC#1,

and wherein:

all the resins are as identified in Example 1 & 7 above.

The tape was made and oriented into 16-inch wide tubing film by aprocess as described above in Example 1. Although the tape orientedacceptably, the orientability of the tape was inferior to theorientability of the tape of Example 1, probably because the tape ofExample 1 contained a core layer comprising a more preferred nyloncomposition.

The casing film, made as described immediately above, was then slit intofilm sheet and corona treated and backseamed in the manner described inExample 12, above. The film backseamed acceptably. The resultinglap-seal backseamed casing was then shirred, with the shirred casingthen being evaluated for seal strength. The results indicated that whilethe seal strength of the shirred casings was good, the shirring processresulted in a low but more than preferred rate of formation of pinholesalongside the backseam.

The results obtained from Examples 1-6, which are according to thepresent invention, as well as the results obtained from Examples 7-14,reveal several important and unexpected results obtained by the presentinvention.

First, it has been discovered that a core layer of nylon substantiallyreduces, or prevents, film neck-down on the forming shoe during thebackseaming process, so long as the nylon core layer has at least acertain minimum thickness. While the amount of nylon needed probablydepends on a variety of factors, such as composition of the remainder ofthe film, overall physical properties, etc., it appears that the nylonlayer needs to have a thickness of at least about 5%, based on the totalthickness of the multilayer film, if necking down on the forming shoe isto be substantially reduced or prevented.

Second, the selection of the type of nylon can have a significant impacton the performance of the film, not just with regard to backseamability,but also with regard to other desired characteristics, such as improvedorientability, improved sealability, improved seal strength, andimproved pinhole-resistance. Whereas seal strength is simply thestrength of the seal as measured by ability to withstand cook-in,sealability is the ease of sealing, i.e., incorporates a sealing windowtemperature, seal consistency between batches, and seal reliabilityduring cook-in. For example, a comparison of the performance of thebackseamed casings according to Example 6 versus Example 11 reveals thatthe core layer of a blend of nylon 6 (50%) and nylon 6/12 (50%),provides better tape orientability, better sealability, betterbackseamability, and better seal strength. The influence of the nyloncore layer on backseamability is unexpected in that it cannot beexplained by the modulus, free shrink, or shrink force imparted by thenylon-containing layer. Moreover, the significant influence of the nyloncore layer on seal strength is unexpected in that the nylon core layeris not serving as a sealant layer.

Third, a comparison of Examples 12-14 with themselves and with Examples1-11 indicates several advantages of the backseamed casing according tothe present invention. First, although the core layer comprisingpolyester and/or first nylon, or first nylon having a melting point ofat least 300° F., provides advantages in backseamability, i.e., ofprevention of necking down on the forming shoe, this advantage can insome cases (depending on the remainder of the film composition) beobtained even without the presence of such a core layer, as is apparentfrom a comparison of Example 12 (Comparative) with Example 13. Second, acomparison of Example 13 with Examples 1 and 5 indicates that even if anylon core layer is present and the film backseams acceptably, outerlayers comprising propylene/ethylene copolymers are associated with sealpuckering, which is aesthetically and commercially less than preferred,as well as a less than preferred level of seal cook-in survival. Third,a comparison of Example 14 with Examples 1 and 5 indicates that thecasings according to Examples 1 and 5 shirred without detectable pinholeformation, in contrast to the comparative casing of Example 14. Also, acomparison of Examples 6, 13, and 14 with Examples 1 and 5, indicatesthat a more preferred nylon composition can significantly enhance theorientability of the tape during the formation of the film tubing.

Although the present invention has been described with reference to thepreferred embodiments, it is to be understood that modifications andvariations of the invention exist without departing from the principlesand scope of the invention, as those skilled in the art will readilyunderstand. Accordingly, such modifications are in accordance with theclaims set forth below.

What is claimed is:
 1. A backseamed casing comprising a heat-shrinkablecasing film comprising: (A) a first outer layer serving as an insidecasing layer, the first outer layer comprising a first polyolefin, thefirst polyolefin having a surface energy level of less than 34 dynes/cm;(B) a second layer comprising at least one member selected from thegroup consisting of polyester and first polyamide; (C) a third layerserving as an outside casing layer, the third outer layer comprising atleast one member selected from the group consisting of a secondpolyolefin, polystyrene and second polyamide; and wherein the secondlayer is between the first layer and the third layer, and the secondlayer has a thickness of at least 5% of a total thickness of theheat-shrinkable easing film, the second layer comprising an amount ofpolyamide and/or polyester effective to prevent the casing film fromnecking down against a forming shoe to an extent that the casing filmruptures or cannot be forwarded during backseaming.
 2. The backseamedcasing according to claim 1, wherein the third layer comprises thesecond polyolefin.
 3. The backseamed casing according to claim 1,wherein the second layer comprises the first polyamide.
 4. Thebackseamed casing according to claim 1, wherein the first polyolefincomprises at least one member selected from the group consisting ofpolyethylene homopolymer, polyethylene copolymer, polypropylenehomopolymer, polypropylene copolymer, polybutene homopolymer, andpolybutene copolymer.
 5. The backseamed casing according to claim 4,wherein the first polyolefin comprises at least one member selected fromthe group consisting of ethylene/alpha-olefin copolymer,propylene/alpha-olefin copolymer, butene/alpha-olefin copolymer,ethylene/unsaturated acid copolymer, and ethylene/unsaturated estercopolymer.
 6. The backseamed casing according to claim 5, wherein thefirst polyolefin comprises at least one member selected from the groupconsisting of linear low density polyethylene, propylene/ethylenecopolymer, and propylene/butene copolymer.
 7. The backseamed casingaccording to claim 4, wherein the first polyolefin comprises linear lowdensity polyethylene.
 8. The backseamed casing according to claim 1,wherein the second layer has a thickness of from about 5 to 50 percent,based on a total thickness of the multilayer film.
 9. The backseamedcasing according to claim 8, wherein the second layer has a thickness offrom about 5 to 40 percent, based on a total thickness of the multilayerfilm.
 10. The backseamed casing according to claim 9, wherein the secondlayer has a thickness of from about 10 to 30 percent, based on a totalthickness of the multilayer film.
 11. The backseamed casing according toclaim 9, wherein the second layer has a thickness of from about 5 to 20percent, based on a total thickness of the multilayer film.
 12. Thebackseamed casing according to claim 1, wherein the third layercomprises the second polyamide.
 13. The backseamed casing according toclaim 1, wherein the second layer comprises the first polyamide, and thefirst polyamide comprises at least one member selected from the groupconsisting of polyamide 6, polyamide 66, polyamide 9, polyamide 10,polyamide 11, polyamide 12, polyamide 69, polyamide 610, polyamide 612,polyamide 6I, polyamide 6T, and copolymers thereof.
 14. The backseamedcasing according to claim 13, wherein the first polyamide comprises atleast one member selected from the group consisting of polyamide 6,polyamide 66 and copolyamide 6/66.
 15. The backseamed casing accordingto claim 14, wherein the first polyamide comprises copolyamide 6/66. 16.The backseamed casing according to claim 13, wherein the second layerconsists essentially of at least one member selected from the groupconsisting of polyamide 6, polyamide 66, polyamide 9, polyamide 10,polyamide 11, polyamide 12, polyamide 69, polyamide 610, polyamide 612,polyamide 6I, polyamide 6T, and copolymers thereof.
 17. The backseamedcasing according to claim 1, wherein the heat-shrinkable casing film hasbiaxial orientation.
 18. The backseamed casing according to claim 1,wherein the casing film has a free shrink, at 185° F., of from 5 to 70percent in at least one direction.
 19. The backseamed casing accordingto claim 1, wherein the casing film has a free shrink, at 185° F., of atleast 10 percent in at least one direction.
 20. The backseamed casingaccording to claim 1, wherein the casing film has a free shrink, at1850° F., of from 15 to 35 percent in at least one direction.
 21. Thebackseamed casing according to claim 1, wherein the casing film has atotal free shrink, at 185° F., of from 20 to 50 percent.
 22. Thebackseamed casing according to claim 1, wherein at least a portion ofthe casing film comprises a crosslinked polymer network.
 23. Thebackseamed casing according to claim 1, wherein the backseam casing is alap-seal backseam casing.
 24. The backseamed casing according to claim1, wherein the surface of the first outer layer is treated to provide apolar film surface.
 25. The backseamed casing according to claim 1,wherein the first outer layer of the casing is corona treated.
 26. Thebackseamed casing according to claim 25 wherein the second layercomprises polyamide 6 and the first polyolefin comprises linear lowdensity polyethylene and the casing film is biaxially oriented.